Sergey Senozhatsky improves zram's post-processing selection algorithm.
This leads to improved memory savings.
- Wei Yang has gone to town on the mapletree code, contributing several
series which clean up the implementation:
- "refine mas_mab_cp()"
- "Reduce the space to be cleared for maple_big_node"
- "maple_tree: simplify mas_push_node()"
- "Following cleanup after introduce mas_wr_store_type()"
- "refine storing null"
- The series "selftests/mm: hugetlb_fault_after_madv improvements" from
David Hildenbrand fixes this selftest for s390.
- The series "introduce pte_offset_map_{ro|rw}_nolock()" from Qi Zheng
implements some rationaizations and cleanups in the page mapping code.
- The series "mm: optimize shadow entries removal" from Shakeel Butt
optimizes the file truncation code by speeding up the handling of shadow
entries.
- The series "Remove PageKsm()" from Matthew Wilcox completes the
migration of this flag over to being a folio-based flag.
- The series "Unify hugetlb into arch_get_unmapped_area functions" from
Oscar Salvador implements a bunch of consolidations and cleanups in the
hugetlb code.
- The series "Do not shatter hugezeropage on wp-fault" from Dev Jain
takes away the wp-fault time practice of turning a huge zero page into
small pages. Instead we replace the whole thing with a THP. More
consistent cleaner and potentiall saves a large number of pagefaults.
- The series "percpu: Add a test case and fix for clang" from Andy
Shevchenko enhances and fixes the kernel's built in percpu test code.
- The series "mm/mremap: Remove extra vma tree walk" from Liam Howlett
optimizes mremap() by avoiding doing things which we didn't need to do.
- The series "Improve the tmpfs large folio read performance" from
Baolin Wang teaches tmpfs to copy data into userspace at the folio size
rather than as individual pages. A 20% speedup was observed.
- The series "mm/damon/vaddr: Fix issue in
damon_va_evenly_split_region()" fro Zheng Yejian fixes DAMON splitting.
- The series "memcg-v1: fully deprecate charge moving" from Shakeel Butt
removes the long-deprecated memcgv2 charge moving feature.
- The series "fix error handling in mmap_region() and refactor" from
Lorenzo Stoakes cleanup up some of the mmap() error handling and
addresses some potential performance issues.
- The series "x86/module: use large ROX pages for text allocations" from
Mike Rapoport teaches x86 to use large pages for read-only-execute
module text.
- The series "page allocation tag compression" from Suren Baghdasaryan
is followon maintenance work for the new page allocation profiling
feature.
- The series "page->index removals in mm" from Matthew Wilcox remove
most references to page->index in mm/. A slow march towards shrinking
struct page.
- The series "damon/{self,kunit}tests: minor fixups for DAMON debugfs
interface tests" from Andrew Paniakin performs maintenance work for
DAMON's self testing code.
- The series "mm: zswap swap-out of large folios" from Kanchana Sridhar
improves zswap's batching of compression and decompression. It is a
step along the way towards using Intel IAA hardware acceleration for
this zswap operation.
- The series "kasan: migrate the last module test to kunit" from
Sabyrzhan Tasbolatov completes the migration of the KASAN built-in tests
over to the KUnit framework.
- The series "implement lightweight guard pages" from Lorenzo Stoakes
permits userapace to place fault-generating guard pages within a single
VMA, rather than requiring that multiple VMAs be created for this.
Improved efficiencies for userspace memory allocators are expected.
- The series "memcg: tracepoint for flushing stats" from JP Kobryn uses
tracepoints to provide increased visibility into memcg stats flushing
activity.
- The series "zram: IDLE flag handling fixes" from Sergey Senozhatsky
fixes a zram buglet which potentially affected performance.
- The series "mm: add more kernel parameters to control mTHP" from
Maíra Canal enhances our ability to control/configuremultisize THP from
the kernel boot command line.
- The series "kasan: few improvements on kunit tests" from Sabyrzhan
Tasbolatov has a couple of fixups for the KASAN KUnit tests.
- The series "mm/list_lru: Split list_lru lock into per-cgroup scope"
from Kairui Song optimizes list_lru memory utilization when lockdep is
enabled.
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Merge tag 'mm-stable-2024-11-18-19-27' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Pull MM updates from Andrew Morton:
- The series "zram: optimal post-processing target selection" from
Sergey Senozhatsky improves zram's post-processing selection
algorithm. This leads to improved memory savings.
- Wei Yang has gone to town on the mapletree code, contributing several
series which clean up the implementation:
- "refine mas_mab_cp()"
- "Reduce the space to be cleared for maple_big_node"
- "maple_tree: simplify mas_push_node()"
- "Following cleanup after introduce mas_wr_store_type()"
- "refine storing null"
- The series "selftests/mm: hugetlb_fault_after_madv improvements" from
David Hildenbrand fixes this selftest for s390.
- The series "introduce pte_offset_map_{ro|rw}_nolock()" from Qi Zheng
implements some rationaizations and cleanups in the page mapping
code.
- The series "mm: optimize shadow entries removal" from Shakeel Butt
optimizes the file truncation code by speeding up the handling of
shadow entries.
- The series "Remove PageKsm()" from Matthew Wilcox completes the
migration of this flag over to being a folio-based flag.
- The series "Unify hugetlb into arch_get_unmapped_area functions" from
Oscar Salvador implements a bunch of consolidations and cleanups in
the hugetlb code.
- The series "Do not shatter hugezeropage on wp-fault" from Dev Jain
takes away the wp-fault time practice of turning a huge zero page
into small pages. Instead we replace the whole thing with a THP. More
consistent cleaner and potentiall saves a large number of pagefaults.
- The series "percpu: Add a test case and fix for clang" from Andy
Shevchenko enhances and fixes the kernel's built in percpu test code.
- The series "mm/mremap: Remove extra vma tree walk" from Liam Howlett
optimizes mremap() by avoiding doing things which we didn't need to
do.
- The series "Improve the tmpfs large folio read performance" from
Baolin Wang teaches tmpfs to copy data into userspace at the folio
size rather than as individual pages. A 20% speedup was observed.
- The series "mm/damon/vaddr: Fix issue in
damon_va_evenly_split_region()" fro Zheng Yejian fixes DAMON
splitting.
- The series "memcg-v1: fully deprecate charge moving" from Shakeel
Butt removes the long-deprecated memcgv2 charge moving feature.
- The series "fix error handling in mmap_region() and refactor" from
Lorenzo Stoakes cleanup up some of the mmap() error handling and
addresses some potential performance issues.
- The series "x86/module: use large ROX pages for text allocations"
from Mike Rapoport teaches x86 to use large pages for
read-only-execute module text.
- The series "page allocation tag compression" from Suren Baghdasaryan
is followon maintenance work for the new page allocation profiling
feature.
- The series "page->index removals in mm" from Matthew Wilcox remove
most references to page->index in mm/. A slow march towards shrinking
struct page.
- The series "damon/{self,kunit}tests: minor fixups for DAMON debugfs
interface tests" from Andrew Paniakin performs maintenance work for
DAMON's self testing code.
- The series "mm: zswap swap-out of large folios" from Kanchana Sridhar
improves zswap's batching of compression and decompression. It is a
step along the way towards using Intel IAA hardware acceleration for
this zswap operation.
- The series "kasan: migrate the last module test to kunit" from
Sabyrzhan Tasbolatov completes the migration of the KASAN built-in
tests over to the KUnit framework.
- The series "implement lightweight guard pages" from Lorenzo Stoakes
permits userapace to place fault-generating guard pages within a
single VMA, rather than requiring that multiple VMAs be created for
this. Improved efficiencies for userspace memory allocators are
expected.
- The series "memcg: tracepoint for flushing stats" from JP Kobryn uses
tracepoints to provide increased visibility into memcg stats flushing
activity.
- The series "zram: IDLE flag handling fixes" from Sergey Senozhatsky
fixes a zram buglet which potentially affected performance.
- The series "mm: add more kernel parameters to control mTHP" from
Maíra Canal enhances our ability to control/configuremultisize THP
from the kernel boot command line.
- The series "kasan: few improvements on kunit tests" from Sabyrzhan
Tasbolatov has a couple of fixups for the KASAN KUnit tests.
- The series "mm/list_lru: Split list_lru lock into per-cgroup scope"
from Kairui Song optimizes list_lru memory utilization when lockdep
is enabled.
* tag 'mm-stable-2024-11-18-19-27' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: (215 commits)
cma: enforce non-zero pageblock_order during cma_init_reserved_mem()
mm/kfence: add a new kunit test test_use_after_free_read_nofault()
zram: fix NULL pointer in comp_algorithm_show()
memcg/hugetlb: add hugeTLB counters to memcg
vmstat: call fold_vm_zone_numa_events() before show per zone NUMA event
mm: mmap_lock: check trace_mmap_lock_$type_enabled() instead of regcount
zram: ZRAM_DEF_COMP should depend on ZRAM
MAINTAINERS/MEMORY MANAGEMENT: add document files for mm
Docs/mm/damon: recommend academic papers to read and/or cite
mm: define general function pXd_init()
kmemleak: iommu/iova: fix transient kmemleak false positive
mm/list_lru: simplify the list_lru walk callback function
mm/list_lru: split the lock to per-cgroup scope
mm/list_lru: simplify reparenting and initial allocation
mm/list_lru: code clean up for reparenting
mm/list_lru: don't export list_lru_add
mm/list_lru: don't pass unnecessary key parameters
kasan: add kunit tests for kmalloc_track_caller, kmalloc_node_track_caller
kasan: change kasan_atomics kunit test as KUNIT_CASE_SLOW
kasan: use EXPORT_SYMBOL_IF_KUNIT to export symbols
...
Now that page_pgoff() takes const pointers, we can constify the pointers
to a lot of functions.
Link: https://lkml.kernel.org/r/20241005200121.3231142-5-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This function doesn't modify any of its arguments, so if we make a few
other functions take const pointers, we can make page_address_in_vma()
take const pointers too. All of its callers have the containing folio
already, so pass that in as an argument instead of recalculating it. Also
add kernel-doc
Link: https://lkml.kernel.org/r/20241005200121.3231142-4-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
The hugepage parameter was deprecated since commit ddc1a5cbc0
("mempolicy: alloc_pages_mpol() for NUMA policy without vma"), for
PMD-sized THP, it still tries only preferred node if possible in
vma_alloc_folio() by checking the order of the folio allocation.
Link: https://lkml.kernel.org/r/20241010061556.1846751-1-wangkefeng.wang@huawei.com
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Barry Song <baohua@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
All callers have been converted to use folio_test_ksm() or
PageAnonNotKsm(), so we can remove this wrapper.
Link: https://lkml.kernel.org/r/20241002152533.1350629-6-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Alex Shi <alexs@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Remove a call to PageKSM() by passing the folio containing tmp_page to
should_skip_rmap_item. Removes a hidden call to compound_head().
Link: https://lkml.kernel.org/r/20241002152533.1350629-4-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Alex Shi <alexs@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
By making try_to_merge_two_pages() and stable_tree_search() return a
folio, we can replace kpage with kfolio. This replaces 7 calls to
compound_head() with one.
[cuigaosheng1@huawei.com: add IS_ERR_OR_NULL check for stable_tree_search()]
Signed-off-by: Gaosheng Cui <cuigaosheng1@huawei.com>
Link: https://lkml.kernel.org/r/20241002152533.1350629-3-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Alex Shi <alexs@kernel.org>
Cc: Gaosheng Cui <cuigaosheng1@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Patch series "Remove PageKsm()".
The KSM flag is almost always tested on the folio rather than on the page.
This series removes the final users of PageKsm() and makes the flag only
This patch (of 5):
It is safe to use a folio here because all callers took a refcount on this
page. The one wrinkle is that we have to recalculate the value of folio
after splitting the page, since it has probably changed. Replaces nine
calls to compound_head() with one.
Link: https://lkml.kernel.org/r/20241002152533.1350629-1-willy@infradead.org
Link: https://lkml.kernel.org/r/20241002152533.1350629-2-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Alex Shi <alexs@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
The types of mm flags are now far beyond the core dump related features.
This patch moves mm flags from linux/sched/coredump.h to linux/mm_types.h.
The linux/sched/coredump.h has include the mm_types.h, so the C files
related to coredump does not need to change head file inclusion. In
addition, the inclusion of sched/coredump.h now can be deleted from the C
files that irrelevant to core dump.
Link: https://lkml.kernel.org/r/20240926074922.2721274-1-sunnanyong@huawei.com
Signed-off-by: Nanyong Sun <sunnanyong@huawei.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This flag is now only used on folios, so we can remove all the page
accessors and reword the comments that refer to them.
Link: https://lkml.kernel.org/r/20240821193445.2294269-5-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Let's simplify by reusing folio_walk. Keep the existing behavior by
handling migration entries and zeropages.
Link: https://lkml.kernel.org/r/20240802155524.517137-12-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Janosch Frank <frankja@linux.ibm.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Let's use folio_walk instead, for example avoiding taking temporary folio
references if the folio does obviously not even apply and getting rid of
one more follow_page() user. We cannot move all handling under the PTL,
so leave the rmap handling (which implies an allocation) out.
Note that zeropages obviously don't apply: old code could just have
specified FOLL_DUMP. Further, we don't care about losing the secretmem
check in follow_page(): these are never anon pages and
vma_ksm_compatible() would never consider secretmem vmas (VM_SHARED |
VM_MAYSHARE must be set for secretmem, see secretmem_mmap()).
Link: https://lkml.kernel.org/r/20240802155524.517137-7-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Janosch Frank <frankja@linux.ibm.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Let's use folio_walk instead, for example avoiding taking temporary folio
references if the folio does not even apply and getting rid of one more
follow_page() user.
Note that zeropages obviously don't apply: old code could just have
specified FOLL_DUMP. Anon folios are never secretmem, so we don't care
about losing the check in follow_page().
Link: https://lkml.kernel.org/r/20240802155524.517137-6-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Janosch Frank <frankja@linux.ibm.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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Merge tag 'random-6.11-rc1-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/crng/random
Pull random number generator updates from Jason Donenfeld:
"This adds getrandom() support to the vDSO.
First, it adds a new kind of mapping to mmap(2), MAP_DROPPABLE, which
lets the kernel zero out pages anytime under memory pressure, which
enables allocating memory that never gets swapped to disk but also
doesn't count as being mlocked.
Then, the vDSO implementation of getrandom() is introduced in a
generic manner and hooked into random.c.
Next, this is implemented on x86. (Also, though it's not ready for
this pull, somebody has begun an arm64 implementation already)
Finally, two vDSO selftests are added.
There are also two housekeeping cleanup commits"
* tag 'random-6.11-rc1-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/crng/random:
MAINTAINERS: add random.h headers to RNG subsection
random: note that RNDGETPOOL was removed in 2.6.9-rc2
selftests/vDSO: add tests for vgetrandom
x86: vdso: Wire up getrandom() vDSO implementation
random: introduce generic vDSO getrandom() implementation
mm: add MAP_DROPPABLE for designating always lazily freeable mappings
The vDSO getrandom() implementation works with a buffer allocated with a
new system call that has certain requirements:
- It shouldn't be written to core dumps.
* Easy: VM_DONTDUMP.
- It should be zeroed on fork.
* Easy: VM_WIPEONFORK.
- It shouldn't be written to swap.
* Uh-oh: mlock is rlimited.
* Uh-oh: mlock isn't inherited by forks.
- It shouldn't reserve actual memory, but it also shouldn't crash when
page faulting in memory if none is available
* Uh-oh: VM_NORESERVE means segfaults.
It turns out that the vDSO getrandom() function has three really nice
characteristics that we can exploit to solve this problem:
1) Due to being wiped during fork(), the vDSO code is already robust to
having the contents of the pages it reads zeroed out midway through
the function's execution.
2) In the absolute worst case of whatever contingency we're coding for,
we have the option to fallback to the getrandom() syscall, and
everything is fine.
3) The buffers the function uses are only ever useful for a maximum of
60 seconds -- a sort of cache, rather than a long term allocation.
These characteristics mean that we can introduce VM_DROPPABLE, which
has the following semantics:
a) It never is written out to swap.
b) Under memory pressure, mm can just drop the pages (so that they're
zero when read back again).
c) It is inherited by fork.
d) It doesn't count against the mlock budget, since nothing is locked.
e) If there's not enough memory to service a page fault, it's not fatal,
and no signal is sent.
This way, allocations used by vDSO getrandom() can use:
VM_DROPPABLE | VM_DONTDUMP | VM_WIPEONFORK | VM_NORESERVE
And there will be no problem with OOMing, crashing on overcommitment,
using memory when not in use, not wiping on fork(), coredumps, or
writing out to swap.
In order to let vDSO getrandom() use this, expose these via mmap(2) as
MAP_DROPPABLE.
Note that this involves removing the MADV_FREE special case from
sort_folio(), which according to Yu Zhao is unnecessary and will simply
result in an extra call to shrink_folio_list() in the worst case. The
chunk removed reenables the swapbacked flag, which we don't want for
VM_DROPPABLE, and we can't conditionalize it here because there isn't a
vma reference available.
Finally, the provided self test ensures that this is working as desired.
Cc: linux-mm@kvack.org
Acked-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Patch series "mm: migrate: support poison recover from migrate folio", v5.
The folio migration is widely used in kernel, memory compaction, memory
hotplug, soft offline page, numa balance, memory demote/promotion, etc,
but once access a poisoned source folio when migrating, the kernel will
panic.
There is a mechanism in the kernel to recover from uncorrectable memory
errors, ARCH_HAS_COPY_MC(eg, Machine Check Safe Memory Copy on x86), which
is already used in NVDIMM or core-mm paths(eg, CoW, khugepaged, coredump,
ksm copy), see copy_mc_to_{user,kernel}, copy_mc_{user_}highpage callers.
This series of patches provide the recovery mechanism from folio copy for
the widely used folio migration. Please note, because folio migration is
no guarantee of success, so we could chose to make folio migration
tolerant of memory failures, adding folio_mc_copy() which is a #MC
versions of folio_copy(), once accessing a poisoned source folio, we could
return error and make the folio migration fail, and this could avoid the
similar panic shown below.
CPU: 1 PID: 88343 Comm: test_softofflin Kdump: loaded Not tainted 6.6.0
pc : copy_page+0x10/0xc0
lr : copy_highpage+0x38/0x50
...
Call trace:
copy_page+0x10/0xc0
folio_copy+0x78/0x90
migrate_folio_extra+0x54/0xa0
move_to_new_folio+0xd8/0x1f0
migrate_folio_move+0xb8/0x300
migrate_pages_batch+0x528/0x788
migrate_pages_sync+0x8c/0x258
migrate_pages+0x440/0x528
soft_offline_in_use_page+0x2ec/0x3c0
soft_offline_page+0x238/0x310
soft_offline_page_store+0x6c/0xc0
dev_attr_store+0x20/0x40
sysfs_kf_write+0x4c/0x68
kernfs_fop_write_iter+0x130/0x1c8
new_sync_write+0xa4/0x138
vfs_write+0x238/0x2d8
ksys_write+0x74/0x110
This patch (of 5):
There is a memory_failure_queue() call after copy_mc_[user]_highpage(),
see callers, eg, CoW/KSM page copy, it is used to mark the source page as
h/w poisoned and unmap it from other tasks, and the upcomming poison
recover from migrate folio will do the similar thing, so let's move the
memory_failure_queue() into the copy_mc_[user]_highpage() instead of
adding it into each user, this should also enhance the handling of
poisoned page in khugepaged.
Link: https://lkml.kernel.org/r/20240626085328.608006-1-wangkefeng.wang@huawei.com
Link: https://lkml.kernel.org/r/20240626085328.608006-2-wangkefeng.wang@huawei.com
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Reviewed-by: Jane Chu <jane.chu@oracle.com>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Benjamin LaHaise <bcrl@kvack.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jérôme Glisse <jglisse@redhat.com>
Cc: Jiaqi Yan <jiaqiyan@google.com>
Cc: Lance Yang <ioworker0@gmail.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Naoya Horiguchi <nao.horiguchi@gmail.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Now the implementation of stable_node_dup() causes chain()/chain_prune()
interfaces and usages are overcomplicated.
Why? stable_node_dup() only find and return a candidate stable_node for
sharing, so the users have to recheck using stable_node_dup_any() if any
non-candidate stable_node exist. And try to ksm_get_folio() from it
again.
Actually, stable_node_dup() can just return a best stable_node as it can,
then the users can check if it's a candidate for sharing or not.
The code is simplified too and fewer corner cases: such as stable_node and
stable_node_dup can't be NULL if returned tree_folio is not NULL.
Link: https://lkml.kernel.org/r/20240621-b4-ksm-scan-optimize-v2-3-1c328aa9e30b@linux.dev
Signed-off-by: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Stefan Roesch <shr@devkernel.io>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
The code flow in cmp_and_merge_page() is suboptimal for handling the ksm
page and non-ksm page at the same time. For example:
- ksm page
1. Mostly just return if this ksm page is not migrated and this rmap_item
has been on the rmap hlist. Or we have to fix this rmap_item mapping.
2. But we absolutely don't need to checksum for this ksm page, since it
can't change.
- non-ksm page
1. First don't need to waste time searching stable tree if fast changing.
2. Should try to merge with zero page before search the stable tree.
3. Then search stable tree to find mergeable ksm page.
This patch optimizes the code flow so the handling differences between ksm
page and non-ksm page become clearer and more efficient too.
Link: https://lkml.kernel.org/r/20240621-b4-ksm-scan-optimize-v2-2-1c328aa9e30b@linux.dev
Signed-off-by: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Stefan Roesch <shr@devkernel.io>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Patch series "mm/ksm: cmp_and_merge_page() optimizations and cleanup", v2.
This series mainly optimizes cmp_and_merge_page() to have more efficient
separate code flow for ksm page and non-ksm anon page.
- ksm page: don't need to calculate the checksum obviously.
- anon page: don't need to search stable tree if changing fast and try
to merge with zero page before searching ksm page on stable tree.
Please see the patch-2 for details.
Patch-3 is cleanup also a little optimization for the chain()/chain_prune
interfaces, which made the stable_tree_search()/stable_tree_insert() over
complex.
I have done simple testing using "hackbench -g 1 -l 300000" (maybe I need
to use a better workload) on my machine, have seen a little CPU usage
decrease of ksmd and some improvements of cmp_and_merge_page() latency:
We can see the latency of cmp_and_merge_page() when handling non-ksm anon
pages has been improved.
This patch (of 3):
In preparation for later changes, refactor out a new function called
try_to_merge_with_zero_page(), which tries to merge with zero page.
Link: https://lkml.kernel.org/r/20240621-b4-ksm-scan-optimize-v2-0-1c328aa9e30b@linux.dev
Link: https://lkml.kernel.org/r/20240621-b4-ksm-scan-optimize-v2-1-1c328aa9e30b@linux.dev
Signed-off-by: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Stefan Roesch <shr@devkernel.io>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
After commit 21fbd59136 ("ksm: add the ksm prefix to the names of the
ksm private structures"), we could directly use KMEM_CACHE().
Link: https://lkml.kernel.org/r/20240618081201.134985-1-wangkefeng.wang@huawei.com
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Acked-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
We normally ksm_zero_pages++ in ksmd when page is merged with zero page,
but ksm_zero_pages-- is done from page tables side, where there is no any
accessing protection of ksm_zero_pages.
So we can read very exceptional value of ksm_zero_pages in rare cases,
such as -1, which is very confusing to users.
Fix it by changing to use atomic_long_t, and the same case with the
mm->ksm_zero_pages.
Link: https://lkml.kernel.org/r/20240528-b4-ksm-counters-v3-2-34bb358fdc13@linux.dev
Fixes: e2942062e0 ("ksm: count all zero pages placed by KSM")
Fixes: 6080d19f07 ("ksm: add ksm zero pages for each process")
Signed-off-by: Chengming Zhou <chengming.zhou@linux.dev>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Ran Xiaokai <ran.xiaokai@zte.com.cn>
Cc: Stefan Roesch <shr@devkernel.io>
Cc: xu xin <xu.xin16@zte.com.cn>
Cc: Yang Yang <yang.yang29@zte.com.cn>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Patch series "mm/ksm: fix some accounting problems", v3.
We encountered some abnormal ksm_pages_scanned and ksm_zero_pages during
some random tests.
1. ksm_pages_scanned unchanged even ksmd scanning has progress.
2. ksm_zero_pages maybe -1 in some rare cases.
This patch (of 2):
During testing, I found ksm_pages_scanned is unchanged although the
scan_get_next_rmap_item() did return valid rmap_item that is not NULL.
The reason is the scan_get_next_rmap_item() will return NULL after a full
scan, so ksm_do_scan() just return without accounting of the
ksm_pages_scanned.
Fix it by just putting ksm_pages_scanned accounting in that loop, and it
will be accounted more timely if that loop would last for a long time.
Link: https://lkml.kernel.org/r/20240528-b4-ksm-counters-v3-0-34bb358fdc13@linux.dev
Link: https://lkml.kernel.org/r/20240528-b4-ksm-counters-v3-1-34bb358fdc13@linux.dev
Fixes: b348b5fe2b ("mm/ksm: add pages scanned metric")
Signed-off-by: Chengming Zhou <chengming.zhou@linux.dev>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: xu xin <xu.xin16@zte.com.cn>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Ran Xiaokai <ran.xiaokai@zte.com.cn>
Cc: Stefan Roesch <shr@devkernel.io>
Cc: Yang Yang <yang.yang29@zte.com.cn>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
The commit 2c653d0ee2 ("ksm: introduce ksm_max_page_sharing per page
deduplication limit") introduced a possible failure case in the
stable_tree_insert(), where we may free the new allocated stable_node_dup
if we fail to prepare the missing chain node.
Then that kfolio return and unlock with a freed stable_node set... And
any MM activities can come in to access kfolio->mapping, so UAF.
Fix it by moving folio_set_stable_node() to the end after stable_node
is inserted successfully.
Link: https://lkml.kernel.org/r/20240513-b4-ksm-stable-node-uaf-v1-1-f687de76f452@linux.dev
Fixes: 2c653d0ee2 ("ksm: introduce ksm_max_page_sharing per page deduplication limit")
Signed-off-by: Chengming Zhou <chengming.zhou@linux.dev>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Stefan Roesch <shr@devkernel.io>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
documented (hopefully adequately) in the respective changelogs. Notable
series include:
- Lucas Stach has provided some page-mapping
cleanup/consolidation/maintainability work in the series "mm/treewide:
Remove pXd_huge() API".
- In the series "Allow migrate on protnone reference with
MPOL_PREFERRED_MANY policy", Donet Tom has optimized mempolicy's
MPOL_PREFERRED_MANY mode, yielding almost doubled performance in one
test.
- In their series "Memory allocation profiling" Kent Overstreet and
Suren Baghdasaryan have contributed a means of determining (via
/proc/allocinfo) whereabouts in the kernel memory is being allocated:
number of calls and amount of memory.
- Matthew Wilcox has provided the series "Various significant MM
patches" which does a number of rather unrelated things, but in largely
similar code sites.
- In his series "mm: page_alloc: freelist migratetype hygiene" Johannes
Weiner has fixed the page allocator's handling of migratetype requests,
with resulting improvements in compaction efficiency.
- In the series "make the hugetlb migration strategy consistent" Baolin
Wang has fixed a hugetlb migration issue, which should improve hugetlb
allocation reliability.
- Liu Shixin has hit an I/O meltdown caused by readahead in a
memory-tight memcg. Addressed in the series "Fix I/O high when memory
almost met memcg limit".
- In the series "mm/filemap: optimize folio adding and splitting" Kairui
Song has optimized pagecache insertion, yielding ~10% performance
improvement in one test.
- Baoquan He has cleaned up and consolidated the early zone
initialization code in the series "mm/mm_init.c: refactor
free_area_init_core()".
- Baoquan has also redone some MM initializatio code in the series
"mm/init: minor clean up and improvement".
- MM helper cleanups from Christoph Hellwig in his series "remove
follow_pfn".
- More cleanups from Matthew Wilcox in the series "Various page->flags
cleanups".
- Vlastimil Babka has contributed maintainability improvements in the
series "memcg_kmem hooks refactoring".
- More folio conversions and cleanups in Matthew Wilcox's series
"Convert huge_zero_page to huge_zero_folio"
"khugepaged folio conversions"
"Remove page_idle and page_young wrappers"
"Use folio APIs in procfs"
"Clean up __folio_put()"
"Some cleanups for memory-failure"
"Remove page_mapping()"
"More folio compat code removal"
- David Hildenbrand chipped in with "fs/proc/task_mmu: convert hugetlb
functions to work on folis".
- Code consolidation and cleanup work related to GUP's handling of
hugetlbs in Peter Xu's series "mm/gup: Unify hugetlb, part 2".
- Rick Edgecombe has developed some fixes to stack guard gaps in the
series "Cover a guard gap corner case".
- Jinjiang Tu has fixed KSM's behaviour after a fork+exec in the series
"mm/ksm: fix ksm exec support for prctl".
- Baolin Wang has implemented NUMA balancing for multi-size THPs. This
is a simple first-cut implementation for now. The series is "support
multi-size THP numa balancing".
- Cleanups to vma handling helper functions from Matthew Wilcox in the
series "Unify vma_address and vma_pgoff_address".
- Some selftests maintenance work from Dev Jain in the series
"selftests/mm: mremap_test: Optimizations and style fixes".
- Improvements to the swapping of multi-size THPs from Ryan Roberts in
the series "Swap-out mTHP without splitting".
- Kefeng Wang has significantly optimized the handling of arm64's
permission page faults in the series
"arch/mm/fault: accelerate pagefault when badaccess"
"mm: remove arch's private VM_FAULT_BADMAP/BADACCESS"
- GUP cleanups from David Hildenbrand in "mm/gup: consistently call it
GUP-fast".
- hugetlb fault code cleanups from Vishal Moola in "Hugetlb fault path to
use struct vm_fault".
- selftests build fixes from John Hubbard in the series "Fix
selftests/mm build without requiring "make headers"".
- Memory tiering fixes/improvements from Ho-Ren (Jack) Chuang in the
series "Improved Memory Tier Creation for CPUless NUMA Nodes". Fixes
the initialization code so that migration between different memory types
works as intended.
- David Hildenbrand has improved follow_pte() and fixed an errant driver
in the series "mm: follow_pte() improvements and acrn follow_pte()
fixes".
- David also did some cleanup work on large folio mapcounts in his
series "mm: mapcount for large folios + page_mapcount() cleanups".
- Folio conversions in KSM in Alex Shi's series "transfer page to folio
in KSM".
- Barry Song has added some sysfs stats for monitoring multi-size THP's
in the series "mm: add per-order mTHP alloc and swpout counters".
- Some zswap cleanups from Yosry Ahmed in the series "zswap same-filled
and limit checking cleanups".
- Matthew Wilcox has been looking at buffer_head code and found the
documentation to be lacking. The series is "Improve buffer head
documentation".
- Multi-size THPs get more work, this time from Lance Yang. His series
"mm/madvise: enhance lazyfreeing with mTHP in madvise_free" optimizes
the freeing of these things.
- Kemeng Shi has added more userspace-visible writeback instrumentation
in the series "Improve visibility of writeback".
- Kemeng Shi then sent some maintenance work on top in the series "Fix
and cleanups to page-writeback".
- Matthew Wilcox reduces mmap_lock traffic in the anon vma code in the
series "Improve anon_vma scalability for anon VMAs". Intel's test bot
reported an improbable 3x improvement in one test.
- SeongJae Park adds some DAMON feature work in the series
"mm/damon: add a DAMOS filter type for page granularity access recheck"
"selftests/damon: add DAMOS quota goal test"
- Also some maintenance work in the series
"mm/damon/paddr: simplify page level access re-check for pageout"
"mm/damon: misc fixes and improvements"
- David Hildenbrand has disabled some known-to-fail selftests ni the
series "selftests: mm: cow: flag vmsplice() hugetlb tests as XFAIL".
- memcg metadata storage optimizations from Shakeel Butt in "memcg:
reduce memory consumption by memcg stats".
- DAX fixes and maintenance work from Vishal Verma in the series
"dax/bus.c: Fixups for dax-bus locking".
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Merge tag 'mm-stable-2024-05-17-19-19' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Pull mm updates from Andrew Morton:
"The usual shower of singleton fixes and minor series all over MM,
documented (hopefully adequately) in the respective changelogs.
Notable series include:
- Lucas Stach has provided some page-mapping cleanup/consolidation/
maintainability work in the series "mm/treewide: Remove pXd_huge()
API".
- In the series "Allow migrate on protnone reference with
MPOL_PREFERRED_MANY policy", Donet Tom has optimized mempolicy's
MPOL_PREFERRED_MANY mode, yielding almost doubled performance in
one test.
- In their series "Memory allocation profiling" Kent Overstreet and
Suren Baghdasaryan have contributed a means of determining (via
/proc/allocinfo) whereabouts in the kernel memory is being
allocated: number of calls and amount of memory.
- Matthew Wilcox has provided the series "Various significant MM
patches" which does a number of rather unrelated things, but in
largely similar code sites.
- In his series "mm: page_alloc: freelist migratetype hygiene"
Johannes Weiner has fixed the page allocator's handling of
migratetype requests, with resulting improvements in compaction
efficiency.
- In the series "make the hugetlb migration strategy consistent"
Baolin Wang has fixed a hugetlb migration issue, which should
improve hugetlb allocation reliability.
- Liu Shixin has hit an I/O meltdown caused by readahead in a
memory-tight memcg. Addressed in the series "Fix I/O high when
memory almost met memcg limit".
- In the series "mm/filemap: optimize folio adding and splitting"
Kairui Song has optimized pagecache insertion, yielding ~10%
performance improvement in one test.
- Baoquan He has cleaned up and consolidated the early zone
initialization code in the series "mm/mm_init.c: refactor
free_area_init_core()".
- Baoquan has also redone some MM initializatio code in the series
"mm/init: minor clean up and improvement".
- MM helper cleanups from Christoph Hellwig in his series "remove
follow_pfn".
- More cleanups from Matthew Wilcox in the series "Various
page->flags cleanups".
- Vlastimil Babka has contributed maintainability improvements in the
series "memcg_kmem hooks refactoring".
- More folio conversions and cleanups in Matthew Wilcox's series:
"Convert huge_zero_page to huge_zero_folio"
"khugepaged folio conversions"
"Remove page_idle and page_young wrappers"
"Use folio APIs in procfs"
"Clean up __folio_put()"
"Some cleanups for memory-failure"
"Remove page_mapping()"
"More folio compat code removal"
- David Hildenbrand chipped in with "fs/proc/task_mmu: convert
hugetlb functions to work on folis".
- Code consolidation and cleanup work related to GUP's handling of
hugetlbs in Peter Xu's series "mm/gup: Unify hugetlb, part 2".
- Rick Edgecombe has developed some fixes to stack guard gaps in the
series "Cover a guard gap corner case".
- Jinjiang Tu has fixed KSM's behaviour after a fork+exec in the
series "mm/ksm: fix ksm exec support for prctl".
- Baolin Wang has implemented NUMA balancing for multi-size THPs.
This is a simple first-cut implementation for now. The series is
"support multi-size THP numa balancing".
- Cleanups to vma handling helper functions from Matthew Wilcox in
the series "Unify vma_address and vma_pgoff_address".
- Some selftests maintenance work from Dev Jain in the series
"selftests/mm: mremap_test: Optimizations and style fixes".
- Improvements to the swapping of multi-size THPs from Ryan Roberts
in the series "Swap-out mTHP without splitting".
- Kefeng Wang has significantly optimized the handling of arm64's
permission page faults in the series
"arch/mm/fault: accelerate pagefault when badaccess"
"mm: remove arch's private VM_FAULT_BADMAP/BADACCESS"
- GUP cleanups from David Hildenbrand in "mm/gup: consistently call
it GUP-fast".
- hugetlb fault code cleanups from Vishal Moola in "Hugetlb fault
path to use struct vm_fault".
- selftests build fixes from John Hubbard in the series "Fix
selftests/mm build without requiring "make headers"".
- Memory tiering fixes/improvements from Ho-Ren (Jack) Chuang in the
series "Improved Memory Tier Creation for CPUless NUMA Nodes".
Fixes the initialization code so that migration between different
memory types works as intended.
- David Hildenbrand has improved follow_pte() and fixed an errant
driver in the series "mm: follow_pte() improvements and acrn
follow_pte() fixes".
- David also did some cleanup work on large folio mapcounts in his
series "mm: mapcount for large folios + page_mapcount() cleanups".
- Folio conversions in KSM in Alex Shi's series "transfer page to
folio in KSM".
- Barry Song has added some sysfs stats for monitoring multi-size
THP's in the series "mm: add per-order mTHP alloc and swpout
counters".
- Some zswap cleanups from Yosry Ahmed in the series "zswap
same-filled and limit checking cleanups".
- Matthew Wilcox has been looking at buffer_head code and found the
documentation to be lacking. The series is "Improve buffer head
documentation".
- Multi-size THPs get more work, this time from Lance Yang. His
series "mm/madvise: enhance lazyfreeing with mTHP in madvise_free"
optimizes the freeing of these things.
- Kemeng Shi has added more userspace-visible writeback
instrumentation in the series "Improve visibility of writeback".
- Kemeng Shi then sent some maintenance work on top in the series
"Fix and cleanups to page-writeback".
- Matthew Wilcox reduces mmap_lock traffic in the anon vma code in
the series "Improve anon_vma scalability for anon VMAs". Intel's
test bot reported an improbable 3x improvement in one test.
- SeongJae Park adds some DAMON feature work in the series
"mm/damon: add a DAMOS filter type for page granularity access recheck"
"selftests/damon: add DAMOS quota goal test"
- Also some maintenance work in the series
"mm/damon/paddr: simplify page level access re-check for pageout"
"mm/damon: misc fixes and improvements"
- David Hildenbrand has disabled some known-to-fail selftests ni the
series "selftests: mm: cow: flag vmsplice() hugetlb tests as
XFAIL".
- memcg metadata storage optimizations from Shakeel Butt in "memcg:
reduce memory consumption by memcg stats".
- DAX fixes and maintenance work from Vishal Verma in the series
"dax/bus.c: Fixups for dax-bus locking""
* tag 'mm-stable-2024-05-17-19-19' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: (426 commits)
memcg, oom: cleanup unused memcg_oom_gfp_mask and memcg_oom_order
selftests/mm: hugetlb_madv_vs_map: avoid test skipping by querying hugepage size at runtime
mm/hugetlb: add missing VM_FAULT_SET_HINDEX in hugetlb_wp
mm/hugetlb: add missing VM_FAULT_SET_HINDEX in hugetlb_fault
selftests: cgroup: add tests to verify the zswap writeback path
mm: memcg: make alloc_mem_cgroup_per_node_info() return bool
mm/damon/core: fix return value from damos_wmark_metric_value
mm: do not update memcg stats for NR_{FILE/SHMEM}_PMDMAPPED
selftests: cgroup: remove redundant enabling of memory controller
Docs/mm/damon/maintainer-profile: allow posting patches based on damon/next tree
Docs/mm/damon/maintainer-profile: change the maintainer's timezone from PST to PT
Docs/mm/damon/design: use a list for supported filters
Docs/admin-guide/mm/damon/usage: fix wrong schemes effective quota update command
Docs/admin-guide/mm/damon/usage: fix wrong example of DAMOS filter matching sysfs file
selftests/damon: classify tests for functionalities and regressions
selftests/damon/_damon_sysfs: use 'is' instead of '==' for 'None'
selftests/damon/_damon_sysfs: find sysfs mount point from /proc/mounts
selftests/damon/_damon_sysfs: check errors from nr_schemes file reads
mm/damon/core: initialize ->esz_bp from damos_quota_init_priv()
selftests/damon: add a test for DAMOS quota goal
...
We've already calculated it, so pass it in instead of recalculating it in
collect_procs_ksm().
Link: https://lkml.kernel.org/r/20240412193510.2356957-12-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Jane Chu <jane.chu@oracle.com>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Oscar Salvador <osalvador@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
We want to limit the use of page_mapcount() to the places where it is
absolutely necessary.
If our folio has a stable node, it is a (small) KSM folio -- see
folio_stable_node(). Let's use folio_mapcount() in stable_tree_search()
instead, which results in no functional change.
The mapcount > 1 check is a bit confusing, because that's usually a check
for page sharing. Looks like the reason is that we are guaranteed to not
exceed ksm_max_page_sharing for the tree KSM folio when merging with that.
Let's update the documentation to make that clearer.
Link: https://lkml.kernel.org/r/20240416172533.663418-1-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Alex Shi <alexs@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Only single page could be reached where we set stable node after write
protect, so use folio converted func to replace page's. And remove the
unused func set_page_stable_node().
Link: https://lkml.kernel.org/r/20240411061713.1847574-11-alexs@kernel.org
Signed-off-by: Alex Shi (tencent) <alexs@kernel.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Izik Eidus <izik.eidus@ravellosystems.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
As we are removing get_ksm_page_flags(), make the flags match the new
function name.
Link: https://lkml.kernel.org/r/20240411061713.1847574-10-alexs@kernel.org
Signed-off-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Alex Shi <alexs@kernel.org>
Reviewed-by: Alex Shi <alexs@kernel.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@sous-sol.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Izik Eidus <izik.eidus@ravellosystems.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
In ksm stable tree all page are single, let's convert them to use and
folios as well as stable_tree_insert/stable_tree_search funcs. And
replace get_ksm_page() by ksm_get_folio() since there is no more needs.
It could save a few compound_head calls.
Link: https://lkml.kernel.org/r/20240411061713.1847574-9-alexs@kernel.org
Signed-off-by: Alex Shi (tencent) <alexs@kernel.org>
Cc: Izik Eidus <izik.eidus@ravellosystems.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Chris Wright <chrisw@sous-sol.org>
Cc: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Compound page is checked and skipped before write_protect_page() called,
use folio to save a few compound_head checks.
Link: https://lkml.kernel.org/r/20240411061713.1847574-8-alexs@kernel.org
Signed-off-by: Alex Shi (tencent) <alexs@kernel.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Izik Eidus <izik.eidus@ravellosystems.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Save a compound_head call.
Link: https://lkml.kernel.org/r/20240411061713.1847574-7-alexs@kernel.org
Signed-off-by: Alex Shi (tencent) <alexs@kernel.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Izik Eidus <izik.eidus@ravellosystems.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Use ksm_get_folio() and save 2 compound_head calls.
Link: https://lkml.kernel.org/r/20240411061713.1847574-6-alexs@kernel.org
Signed-off-by: Alex Shi (tencent) <alexs@kernel.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Izik Eidus <izik.eidus@ravellosystems.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Pages in stable tree are all single normal page, so uses ksm_get_folio()
and folio_set_stable_node(), also saves 3 calls to compound_head().
Link: https://lkml.kernel.org/r/20240411061713.1847574-5-alexs@kernel.org
Signed-off-by: Alex Shi (tencent) <alexs@kernel.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Izik Eidus <izik.eidus@ravellosystems.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Turn set_page_stable_node() into a wrapper folio_set_stable_node, and then
use it to replace the former. we will merge them together after all place
converted to folio.
Link: https://lkml.kernel.org/r/20240411061713.1847574-4-alexs@kernel.org
Signed-off-by: Alex Shi (tencent) <alexs@kernel.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Izik Eidus <izik.eidus@ravellosystems.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
To save 2 compound_head calls.
Link: https://lkml.kernel.org/r/20240411061713.1847574-3-alexs@kernel.org
Signed-off-by: Alex Shi (tencent) <alexs@kernel.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Izik Eidus <izik.eidus@ravellosystems.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Patch series "transfer page to folio in KSM".
This is the first part of page to folio transfer on KSM. Since only
single page could be stored in KSM, we could safely transfer stable tree
pages to folios.
This patchset could reduce ksm.o 57kbytes from 2541776 bytes on latest
akpm/mm-stable branch with CONFIG_DEBUG_VM enabled. It pass the KSM
testing in LTP and kernel selftest.
Thanks for Matthew Wilcox and David Hildenbrand's suggestions and
comments!
This patch (of 10):
The ksm only contains single pages, so we could add a new func
ksm_get_folio for get_ksm_page to use folio instead of pages to save a
couple of compound_head calls.
After all caller replaced, get_ksm_page will be removed.
Link: https://lkml.kernel.org/r/20240411061713.1847574-1-alexs@kernel.org
Link: https://lkml.kernel.org/r/20240411061713.1847574-2-alexs@kernel.org
Signed-off-by: Alex Shi (tencent) <alexs@kernel.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Izik Eidus <izik.eidus@ravellosystems.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
With the demise of the .change_pte() MMU notifier callback, there is no
notification happening in set_pte_at_notify(). It is a synonym of
set_pte_at() and can be replaced with it.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20240405115815.3226315-5-pbonzini@redhat.com>
Acked-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Let's convert it like we converted all the other rmap functions. Don't
introduce folio_try_share_anon_rmap_ptes() for now, as we don't have a
user that wants rmap batching in sight. Pretty easy to add later.
All users are easy to convert -- only ksm.c doesn't use folios yet but
that is left for future work -- so let's just do it in a single shot.
While at it, turn the BUG_ON into a WARN_ON_ONCE.
Note that page_try_share_anon_rmap() so far didn't care about pte/pmd
mappings (no compound parameter). We're changing that so we can perform
better sanity checks and make the code actually more readable/consistent.
For example, __folio_rmap_sanity_checks() will make sure that a PMD range
actually falls completely into the folio.
Link: https://lkml.kernel.org/r/20231220224504.646757-39-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Yin Fengwei <fengwei.yin@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Let's convert replace_page(). While at it, perform some folio conversion.
Link: https://lkml.kernel.org/r/20231220224504.646757-19-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Yin Fengwei <fengwei.yin@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This adds a new tracepoint for the ksm advisor. It reports the last scan
time, the new setting of the pages_to_scan parameter and the average cpu
percent usage of the ksmd background thread for the last scan.
Link: https://lkml.kernel.org/r/20231218231054.1625219-4-shr@devkernel.io
Signed-off-by: Stefan Roesch <shr@devkernel.io>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Rik van Riel <riel@surriel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This adds four new knobs for the KSM advisor to influence its behaviour.
The knobs are:
- advisor_mode:
none: no advisor (default)
scan-time: scan time advisor
- advisor_max_cpu: 70 (default, cpu usage percent)
- advisor_min_pages_to_scan: 500 (default)
- advisor_max_pages_to_scan: 30000 (default)
- advisor_target_scan_time: 200 (default in seconds)
The new values will take effect on the next scan round.
Link: https://lkml.kernel.org/r/20231218231054.1625219-3-shr@devkernel.io
Signed-off-by: Stefan Roesch <shr@devkernel.io>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Rik van Riel <riel@surriel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Patch series "mm/ksm: Add ksm advisor", v5.
What is the KSM advisor?
=========================
The ksm advisor automatically manages the pages_to_scan setting to achieve
a target scan time. The target scan time defines how many seconds it
should take to scan all the candidate KSM pages. In other words the
pages_to_scan rate is changed by the advisor to achieve the target scan
time.
Why do we need a KSM advisor?
==============================
The number of candidate pages for KSM is dynamic. It can often be
observed that during the startup of an application more candidate pages
need to be processed. Without an advisor the pages_to_scan parameter
needs to be sized for the maximum number of candidate pages. With the
scan time advisor the pages_to_scan parameter based can be changed based
on demand.
Algorithm
==========
The algorithm calculates the change value based on the target scan time
and the previous scan time. To avoid pertubations an exponentially
weighted moving average is applied.
The algorithm has a max and min
value to:
- guarantee responsiveness to changes
- to limit CPU resource consumption
Parameters to influence the KSM scan advisor
=============================================
The respective parameters are:
- ksm_advisor_mode
0: None (default), 1: scan time advisor
- ksm_advisor_target_scan_time
how many seconds a scan should of all candidate pages take
- ksm_advisor_max_cpu
upper limit for the cpu usage in percent of the ksmd background thread
The initial value and the max value for the pages_to_scan parameter can
be limited with:
- ksm_advisor_min_pages_to_scan
minimum value for pages_to_scan per batch
- ksm_advisor_max_pages_to_scan
maximum value for pages_to_scan per batch
The default settings for the above two parameters should be suitable for
most workloads.
The parameters are exposed as knobs in /sys/kernel/mm/ksm. By default the
scan time advisor is disabled.
Currently there are two advisors:
- none and
- scan-time.
Resource savings
=================
Tests with various workloads have shown considerable CPU savings. Most
of the workloads I have investigated have more candidate pages during
startup. Once the workload is stable in terms of memory, the number of
candidate pages is reduced. Without the advisor, the pages_to_scan needs
to be sized for the maximum number of candidate pages. So having this
advisor definitely helps in reducing CPU consumption.
For the instagram workload, the advisor achieves a 25% CPU reduction.
Once the memory is stable, the pages_to_scan parameter gets reduced to
about 40% of its max value.
The new advisor works especially well if the smart scan feature is also
enabled.
How is defining a target scan time better?
===========================================
For an administrator it is more logical to set a target scan time.. The
administrator can determine how many pages are scanned on each scan.
Therefore setting a target scan time makes more sense.
In addition the administrator might have a good idea about the memory
sizing of its respective workloads.
Setting cpu limits is easier than setting The pages_to_scan parameter. The
pages_to_scan parameter is per batch. For the administrator it is difficult
to set the pages_to_scan parameter.
Tracing
=======
A new tracing event has been added for the scan time advisor. The new
trace event is called ksm_advisor. It reports the scan time, the new
pages_to_scan setting and the cpu usage of the ksmd background thread.
Other approaches
=================
Approach 1: Adapt pages_to_scan after processing each batch. If KSM
merges pages, increase the scan rate, if less KSM pages, reduce the
the pages_to_scan rate. This doesn't work too well. While it increases
the pages_to_scan for a short period, but generally it ends up with a
too low pages_to_scan rate.
Approach 2: Adapt pages_to_scan after each scan. The problem with that
approach is that the calculated scan rate tends to be high. The more
aggressive KSM scans, the more pages it can de-duplicate.
There have been earlier attempts at an advisor:
propose auto-run mode of ksm and its tests
(https://marc.info/?l=linux-mm&m=166029880214485&w=2)
This patch (of 5):
This adds the ksm advisor. The ksm advisor automatically manages the
pages_to_scan setting to achieve a target scan time. The target scan time
defines how many seconds it should take to scan all the candidate KSM
pages. In other words the pages_to_scan rate is changed by the advisor to
achieve the target scan time. The algorithm has a max and min value to:
- guarantee responsiveness to changes
- limit CPU resource consumption
The respective parameters are:
- ksm_advisor_target_scan_time (how many seconds a scan should take)
- ksm_advisor_max_cpu (maximum value for cpu percent usage)
- ksm_advisor_min_pages (minimum value for pages_to_scan per batch)
- ksm_advisor_max_pages (maximum value for pages_to_scan per batch)
The algorithm calculates the change value based on the target scan time
and the previous scan time. To avoid pertubations an exponentially
weighted moving average is applied.
The advisor is managed by two main parameters: target scan time,
cpu max time for the ksmd background thread. These parameters determine
how aggresive ksmd scans.
In addition there are min and max values for the pages_to_scan parameter
to make sure that its initial and max values are not set too low or too
high. This ensures that it is able to react to changes quickly enough.
The default values are:
- target scan time: 200 secs
- max cpu: 70%
- min pages: 500
- max pages: 30000
By default the advisor is disabled. Currently there are two advisors:
none and scan-time.
Tests with various workloads have shown considerable CPU savings. Most of
the workloads I have investigated have more candidate pages during
startup, once the workload is stable in terms of memory, the number of
candidate pages is reduced. Without the advisor, the pages_to_scan needs
to be sized for the maximum number of candidate pages. So having this
advisor definitely helps in reducing CPU consumption.
For the instagram workload, the advisor achieves a 25% CPU reduction.
Once the memory is stable, the pages_to_scan parameter gets reduced to
about 40% of its max value.
Link: https://lkml.kernel.org/r/20231218231054.1625219-1-shr@devkernel.io
Link: https://lkml.kernel.org/r/20231218231054.1625219-2-shr@devkernel.io
Signed-off-by: Stefan Roesch <shr@devkernel.io>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: Stefan Roesch <shr@devkernel.io>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Patch series "Finish two folio conversions".
Most callers of page_add_new_anon_rmap() and
lru_cache_add_inactive_or_unevictable() have been converted to their folio
equivalents, but there are still a few stragglers. There's a bit of
preparatory work in ksm and unuse_pte(), but after that it's pretty
mechanical.
This patch (of 9):
Accept a folio as an argument and return a folio result. Removes a call
to compound_head() in do_swap_page(), and prevents folio & page from
getting out of sync in unuse_pte().
Reviewed-by: David Hildenbrand <david@redhat.com>
[willy@infradead.org: fix smatch warning]
Link: https://lkml.kernel.org/r/ZXnPtblC6A1IkyAB@casper.infradead.org
[david@redhat.com: only adjust the page if the folio changed]
Link: https://lkml.kernel.org/r/6a8f2110-fa91-4c10-9eae-88315309a6e3@redhat.com
Link: https://lkml.kernel.org/r/20231211162214.2146080-1-willy@infradead.org
Link: https://lkml.kernel.org/r/20231211162214.2146080-2-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
A freezable kernel thread can enter frozen state during freezing by
either calling try_to_freeze() or using wait_event_freezable() and its
variants. However, there is no need to use both methods simultaneously.
Link: https://lkml.kernel.org/r/20231213090906.1070985-1-haokexin@gmail.com
Signed-off-by: Kevin Hao <haokexin@gmail.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Patch series "mm: cleanup and use more folio in page fault", v3.
Rename page_copy_prealloc() to folio_prealloc(), which is used by more
functions, also do more folio conversion in page fault.
This patch (of 5):
Since ksm only support normal page, no swapout/in for ksm large folio too,
add large folio check in ksm_might_need_to_copy(), also convert
page->index to folio->index as page->index is going away.
Then convert ksm_might_need_to_copy() to use more folio api to save nine
compound_head() calls, short 'address' to reduce max-line-length.
Link: https://lkml.kernel.org/r/20231118023232.1409103-1-wangkefeng.wang@huawei.com
Link: https://lkml.kernel.org/r/20231118023232.1409103-2-wangkefeng.wang@huawei.com
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Cc: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
kmap_atomic() has been deprecated in favor of kmap_local_page().
Therefore, replace kmap_atomic() with kmap_local_page() in
calc_checksum().
kmap_atomic() is implemented like a kmap_local_page() which also disables
page-faults and preemption (the latter only in !PREEMPT_RT kernels). The
kernel virtual addresses returned by these two API are only valid in the
context of the callers (i.e., they cannot be handed to other threads).
With kmap_local_page() the mappings are per thread and CPU local like in
kmap_atomic(); however, they can handle page-faults and can be called from
any context (including interrupts). The tasks that call kmap_local_page()
can be preempted and, when they are scheduled to run again, the kernel
virtual addresses are restored and are still valid.
In calc_checksum(), the block of code between the mapping and un-mapping
does not depend on the above-mentioned side effects of kmap_aatomic(), so
that a mere replacements of the old API with the new one is all that is
required (i.e., there is no need to explicitly call pagefault_disable()
and/or preempt_disable()).
Link: https://lkml.kernel.org/r/20231120141855.6761-1-fmdefrancesco@gmail.com
Signed-off-by: Fabio M. De Francesco <fabio.maria.de.francesco@linux.intel.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Commit c33c794828 ("mm: ptep_get() conversion") converted all (non-arch)
call sites to use ptep_get() instead of doing a direct dereference of the
pte. Full rationale can be found in that commit's log.
Since then, three new call sites have snuck in, which directly dereference
the pte, so let's fix those up.
Unfortunately there is no reliable automated mechanism to catch these; I'm
relying on a combination of Coccinelle (which throws up a lot of false
positives) and some compiler magic to force a compiler error on
dereference (While this approach finds dereferences, it also yields a
non-booting kernel so can't be committed).
Link: https://lkml.kernel.org/r/20231114154945.490401-1-ryan.roberts@arm.com
Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This change adds the "pages skipped" metric. To be able to evaluate how
successful smart page scanning is, the pages skipped metric can be
compared to the pages scanned metric.
The pages skipped metric is a cumulative counter. The counter is stored
under /sys/kernel/mm/ksm/pages_skipped.
Link: https://lkml.kernel.org/r/20230926040939.516161-3-shr@devkernel.io
Signed-off-by: Stefan Roesch <shr@devkernel.io>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Rik van Riel <riel@surriel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Patch series "Smart scanning mode for KSM", v3.
This patch series adds "smart scanning" for KSM.
What is smart scanning?
=======================
KSM evaluates all the candidate pages for each scan. It does not use historic
information from previous scans. This has the effect that candidate pages that
couldn't be used for KSM de-duplication continue to be evaluated for each scan.
The idea of "smart scanning" is to keep historic information. With the historic
information we can temporarily skip the candidate page for one or several scans.
Details:
========
"Smart scanning" is to keep two small counters to store if the page has been
used for KSM. One counter stores how often we already tried to use the page for
KSM and the other counter stores how often we skip a page.
How often we skip the candidate page depends how often a page failed KSM
de-duplication. The code skips a maximum of 8 times. During testing this has
shown to be a good compromise for different workloads.
New sysfs knob:
===============
Smart scanning is not enabled by default. With /sys/kernel/mm/ksm/smart_scan
smart scanning can be enabled.
Monitoring:
===========
To monitor how effective smart scanning is a new sysfs knob has been introduced.
/sys/kernel/mm/pages_skipped report how many pages have been skipped by smart
scanning.
Results:
========
- Various workloads have shown a 20% - 25% reduction in page scans
For the instagram workload for instance, the number of pages scanned has been
reduced from over 20M pages per scan to less than 15M pages.
- Less pages scans also resulted in an overall higher de-duplication rate as
some shorter lived pages could be de-duplicated additionally
- Less pages scanned allows to reduce the pages_to_scan parameter
and this resulted in a 25% reduction in terms of CPU.
- The improvements have been observed for workloads that enable KSM with
madvise as well as prctl
This patch (of 4):
This change adds a "smart" page scanning mode for KSM. So far all the
candidate pages are continuously scanned to find candidates for
de-duplication. There are a considerably number of pages that cannot be
de-duplicated. This is costly in terms of CPU. By using smart scanning
considerable CPU savings can be achieved.
This change takes the history of scanning pages into account and skips the
page scanning of certain pages for a while if de-deduplication for this
page has not been successful in the past.
To do this it introduces two new fields in the ksm_rmap_item structure:
age and remaining_skips. age, is the KSM age and remaining_skips
determines how often scanning of this page is skipped. The age field is
incremented each time the page is scanned and the page cannot be de-
duplicated. age updated is capped at U8_MAX.
How often a page is skipped is dependent how often de-duplication has been
tried so far and the number of skips is currently limited to 8. This
value has shown to be effective with different workloads.
The feature is currently disable by default and can be enabled with the
new smart_scan knob.
The feature has shown to be very effective: upt to 25% of the page scans
can be eliminated; the pages_to_scan rate can be reduced by 40 - 50% and a
similar de-duplication rate can be maintained.
[akpm@linux-foundation.org: make ksm_smart_scan default true, for testing]
Link: https://lkml.kernel.org/r/20230926040939.516161-1-shr@devkernel.io
Link: https://lkml.kernel.org/r/20230926040939.516161-2-shr@devkernel.io
Signed-off-by: Stefan Roesch <shr@devkernel.io>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: Stefan Roesch <shr@devkernel.io>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
