2017-11-01 15:08:43 +01:00
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/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
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2009-05-13 22:56:24 +00:00
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#ifndef __ASM_GENERIC_MMAN_COMMON_H
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#define __ASM_GENERIC_MMAN_COMMON_H
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2006-02-15 15:17:39 -08:00
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/*
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Author: Michael S. Tsirkin <mst@mellanox.co.il>, Mellanox Technologies Ltd.
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Based on: asm-xxx/mman.h
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*/
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#define PROT_READ 0x1 /* page can be read */
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#define PROT_WRITE 0x2 /* page can be written */
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#define PROT_EXEC 0x4 /* page can be executed */
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#define PROT_SEM 0x8 /* page may be used for atomic ops */
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2019-12-11 18:40:06 +00:00
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/* 0x10 reserved for arch-specific use */
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/* 0x20 reserved for arch-specific use */
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2006-02-15 15:17:39 -08:00
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#define PROT_NONE 0x0 /* page can not be accessed */
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#define PROT_GROWSDOWN 0x01000000 /* mprotect flag: extend change to start of growsdown vma */
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#define PROT_GROWSUP 0x02000000 /* mprotect flag: extend change to end of growsup vma */
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2019-02-08 01:02:55 -05:00
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/* 0x01 - 0x03 are defined in linux/mman.h */
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2006-02-15 15:17:39 -08:00
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#define MAP_TYPE 0x0f /* Mask for type of mapping */
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#define MAP_FIXED 0x10 /* Interpret addr exactly */
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#define MAP_ANONYMOUS 0x20 /* don't use a file */
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2018-04-10 16:36:01 -07:00
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2019-07-16 16:30:41 -07:00
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/* 0x0100 - 0x4000 flags are defined in asm-generic/mman.h */
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#define MAP_POPULATE 0x008000 /* populate (prefault) pagetables */
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#define MAP_NONBLOCK 0x010000 /* do not block on IO */
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#define MAP_STACK 0x020000 /* give out an address that is best suited for process/thread stacks */
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#define MAP_HUGETLB 0x040000 /* create a huge page mapping */
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2019-07-16 16:30:38 -07:00
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#define MAP_SYNC 0x080000 /* perform synchronous page faults for the mapping */
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2018-04-10 16:36:01 -07:00
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#define MAP_FIXED_NOREPLACE 0x100000 /* MAP_FIXED which doesn't unmap underlying mapping */
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2006-02-15 15:17:39 -08:00
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2019-07-16 16:26:27 -07:00
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#define MAP_UNINITIALIZED 0x4000000 /* For anonymous mmap, memory could be
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* uninitialized */
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2015-11-05 18:51:39 -08:00
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/*
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* Flags for mlock
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*/
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#define MLOCK_ONFAULT 0x01 /* Lock pages in range after they are faulted in, do not prefault */
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2006-02-15 15:17:39 -08:00
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#define MS_ASYNC 1 /* sync memory asynchronously */
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#define MS_INVALIDATE 2 /* invalidate the caches */
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#define MS_SYNC 4 /* synchronous memory sync */
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#define MADV_NORMAL 0 /* no further special treatment */
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#define MADV_RANDOM 1 /* expect random page references */
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#define MADV_SEQUENTIAL 2 /* expect sequential page references */
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#define MADV_WILLNEED 3 /* will need these pages */
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#define MADV_DONTNEED 4 /* don't need these pages */
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/* common parameters: try to keep these consistent across architectures */
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2016-01-15 16:55:02 -08:00
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#define MADV_FREE 8 /* free pages only if memory pressure */
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2006-02-15 15:17:39 -08:00
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#define MADV_REMOVE 9 /* remove these pages & resources */
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#define MADV_DONTFORK 10 /* don't inherit across fork */
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#define MADV_DOFORK 11 /* do inherit across fork */
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2009-09-16 11:50:17 +02:00
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#define MADV_HWPOISON 100 /* poison a page for testing */
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2009-12-16 12:20:00 +01:00
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#define MADV_SOFT_OFFLINE 101 /* soft offline page for testing */
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2006-02-15 15:17:39 -08:00
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2009-09-21 17:01:53 -07:00
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#define MADV_MERGEABLE 12 /* KSM may merge identical pages */
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#define MADV_UNMERGEABLE 13 /* KSM may not merge identical pages */
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2011-01-13 15:46:31 -08:00
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#define MADV_HUGEPAGE 14 /* Worth backing with hugepages */
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2011-01-13 15:47:17 -08:00
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#define MADV_NOHUGEPAGE 15 /* Not worth backing with hugepages */
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2011-01-13 15:46:31 -08:00
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2012-03-23 15:02:51 -07:00
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#define MADV_DONTDUMP 16 /* Explicity exclude from the core dump,
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overrides the coredump filter bits */
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2014-04-07 15:37:56 -07:00
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#define MADV_DODUMP 17 /* Clear the MADV_DONTDUMP flag */
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2012-03-23 15:02:51 -07:00
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mm,fork: introduce MADV_WIPEONFORK
Introduce MADV_WIPEONFORK semantics, which result in a VMA being empty
in the child process after fork. This differs from MADV_DONTFORK in one
important way.
If a child process accesses memory that was MADV_WIPEONFORK, it will get
zeroes. The address ranges are still valid, they are just empty.
If a child process accesses memory that was MADV_DONTFORK, it will get a
segmentation fault, since those address ranges are no longer valid in
the child after fork.
Since MADV_DONTFORK also seems to be used to allow very large programs
to fork in systems with strict memory overcommit restrictions, changing
the semantics of MADV_DONTFORK might break existing programs.
MADV_WIPEONFORK only works on private, anonymous VMAs.
The use case is libraries that store or cache information, and want to
know that they need to regenerate it in the child process after fork.
Examples of this would be:
- systemd/pulseaudio API checks (fail after fork) (replacing a getpid
check, which is too slow without a PID cache)
- PKCS#11 API reinitialization check (mandated by specification)
- glibc's upcoming PRNG (reseed after fork)
- OpenSSL PRNG (reseed after fork)
The security benefits of a forking server having a re-inialized PRNG in
every child process are pretty obvious. However, due to libraries
having all kinds of internal state, and programs getting compiled with
many different versions of each library, it is unreasonable to expect
calling programs to re-initialize everything manually after fork.
A further complication is the proliferation of clone flags, programs
bypassing glibc's functions to call clone directly, and programs calling
unshare, causing the glibc pthread_atfork hook to not get called.
It would be better to have the kernel take care of this automatically.
The patch also adds MADV_KEEPONFORK, to undo the effects of a prior
MADV_WIPEONFORK.
This is similar to the OpenBSD minherit syscall with MAP_INHERIT_ZERO:
https://man.openbsd.org/minherit.2
[akpm@linux-foundation.org: numerically order arch/parisc/include/uapi/asm/mman.h #defines]
Link: http://lkml.kernel.org/r/20170811212829.29186-3-riel@redhat.com
Signed-off-by: Rik van Riel <riel@redhat.com>
Reported-by: Florian Weimer <fweimer@redhat.com>
Reported-by: Colm MacCártaigh <colm@allcosts.net>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Helge Deller <deller@gmx.de>
Cc: Kees Cook <keescook@chromium.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Drewry <wad@chromium.org>
Cc: <linux-api@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-09-06 16:25:15 -07:00
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#define MADV_WIPEONFORK 18 /* Zero memory on fork, child only */
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#define MADV_KEEPONFORK 19 /* Undo MADV_WIPEONFORK */
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mm: introduce MADV_COLD
Patch series "Introduce MADV_COLD and MADV_PAGEOUT", v7.
- Background
The Android terminology used for forking a new process and starting an app
from scratch is a cold start, while resuming an existing app is a hot
start. While we continually try to improve the performance of cold
starts, hot starts will always be significantly less power hungry as well
as faster so we are trying to make hot start more likely than cold start.
To increase hot start, Android userspace manages the order that apps
should be killed in a process called ActivityManagerService.
ActivityManagerService tracks every Android app or service that the user
could be interacting with at any time and translates that into a ranked
list for lmkd(low memory killer daemon). They are likely to be killed by
lmkd if the system has to reclaim memory. In that sense they are similar
to entries in any other cache. Those apps are kept alive for
opportunistic performance improvements but those performance improvements
will vary based on the memory requirements of individual workloads.
- Problem
Naturally, cached apps were dominant consumers of memory on the system.
However, they were not significant consumers of swap even though they are
good candidate for swap. Under investigation, swapping out only begins
once the low zone watermark is hit and kswapd wakes up, but the overall
allocation rate in the system might trip lmkd thresholds and cause a
cached process to be killed(we measured performance swapping out vs.
zapping the memory by killing a process. Unsurprisingly, zapping is 10x
times faster even though we use zram which is much faster than real
storage) so kill from lmkd will often satisfy the high zone watermark,
resulting in very few pages actually being moved to swap.
- Approach
The approach we chose was to use a new interface to allow userspace to
proactively reclaim entire processes by leveraging platform information.
This allowed us to bypass the inaccuracy of the kernel’s LRUs for pages
that are known to be cold from userspace and to avoid races with lmkd by
reclaiming apps as soon as they entered the cached state. Additionally,
it could provide many chances for platform to use much information to
optimize memory efficiency.
To achieve the goal, the patchset introduce two new options for madvise.
One is MADV_COLD which will deactivate activated pages and the other is
MADV_PAGEOUT which will reclaim private pages instantly. These new
options complement MADV_DONTNEED and MADV_FREE by adding non-destructive
ways to gain some free memory space. MADV_PAGEOUT is similar to
MADV_DONTNEED in a way that it hints the kernel that memory region is not
currently needed and should be reclaimed immediately; MADV_COLD is similar
to MADV_FREE in a way that it hints the kernel that memory region is not
currently needed and should be reclaimed when memory pressure rises.
This patch (of 5):
When a process expects no accesses to a certain memory range, it could
give a hint to kernel that the pages can be reclaimed when memory pressure
happens but data should be preserved for future use. This could reduce
workingset eviction so it ends up increasing performance.
This patch introduces the new MADV_COLD hint to madvise(2) syscall.
MADV_COLD can be used by a process to mark a memory range as not expected
to be used in the near future. The hint can help kernel in deciding which
pages to evict early during memory pressure.
It works for every LRU pages like MADV_[DONTNEED|FREE]. IOW, It moves
active file page -> inactive file LRU
active anon page -> inacdtive anon LRU
Unlike MADV_FREE, it doesn't move active anonymous pages to inactive file
LRU's head because MADV_COLD is a little bit different symantic.
MADV_FREE means it's okay to discard when the memory pressure because the
content of the page is *garbage* so freeing such pages is almost zero
overhead since we don't need to swap out and access afterward causes just
minor fault. Thus, it would make sense to put those freeable pages in
inactive file LRU to compete other used-once pages. It makes sense for
implmentaion point of view, too because it's not swapbacked memory any
longer until it would be re-dirtied. Even, it could give a bonus to make
them be reclaimed on swapless system. However, MADV_COLD doesn't mean
garbage so reclaiming them requires swap-out/in in the end so it's bigger
cost. Since we have designed VM LRU aging based on cost-model, anonymous
cold pages would be better to position inactive anon's LRU list, not file
LRU. Furthermore, it would help to avoid unnecessary scanning if system
doesn't have a swap device. Let's start simpler way without adding
complexity at this moment. However, keep in mind, too that it's a caveat
that workloads with a lot of pages cache are likely to ignore MADV_COLD on
anonymous memory because we rarely age anonymous LRU lists.
* man-page material
MADV_COLD (since Linux x.x)
Pages in the specified regions will be treated as less-recently-accessed
compared to pages in the system with similar access frequencies. In
contrast to MADV_FREE, the contents of the region are preserved regardless
of subsequent writes to pages.
MADV_COLD cannot be applied to locked pages, Huge TLB pages, or VM_PFNMAP
pages.
[akpm@linux-foundation.org: resolve conflicts with hmm.git]
Link: http://lkml.kernel.org/r/20190726023435.214162-2-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
Reported-by: kbuild test robot <lkp@intel.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: James E.J. Bottomley <James.Bottomley@HansenPartnership.com>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Chris Zankel <chris@zankel.net>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Daniel Colascione <dancol@google.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Hillf Danton <hdanton@sina.com>
Cc: Joel Fernandes (Google) <joel@joelfernandes.org>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Oleksandr Natalenko <oleksandr@redhat.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Sonny Rao <sonnyrao@google.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Tim Murray <timmurray@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-09-25 16:49:08 -07:00
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#define MADV_COLD 20 /* deactivate these pages */
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2019-09-25 16:49:15 -07:00
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#define MADV_PAGEOUT 21 /* reclaim these pages */
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mm: introduce MADV_COLD
Patch series "Introduce MADV_COLD and MADV_PAGEOUT", v7.
- Background
The Android terminology used for forking a new process and starting an app
from scratch is a cold start, while resuming an existing app is a hot
start. While we continually try to improve the performance of cold
starts, hot starts will always be significantly less power hungry as well
as faster so we are trying to make hot start more likely than cold start.
To increase hot start, Android userspace manages the order that apps
should be killed in a process called ActivityManagerService.
ActivityManagerService tracks every Android app or service that the user
could be interacting with at any time and translates that into a ranked
list for lmkd(low memory killer daemon). They are likely to be killed by
lmkd if the system has to reclaim memory. In that sense they are similar
to entries in any other cache. Those apps are kept alive for
opportunistic performance improvements but those performance improvements
will vary based on the memory requirements of individual workloads.
- Problem
Naturally, cached apps were dominant consumers of memory on the system.
However, they were not significant consumers of swap even though they are
good candidate for swap. Under investigation, swapping out only begins
once the low zone watermark is hit and kswapd wakes up, but the overall
allocation rate in the system might trip lmkd thresholds and cause a
cached process to be killed(we measured performance swapping out vs.
zapping the memory by killing a process. Unsurprisingly, zapping is 10x
times faster even though we use zram which is much faster than real
storage) so kill from lmkd will often satisfy the high zone watermark,
resulting in very few pages actually being moved to swap.
- Approach
The approach we chose was to use a new interface to allow userspace to
proactively reclaim entire processes by leveraging platform information.
This allowed us to bypass the inaccuracy of the kernel’s LRUs for pages
that are known to be cold from userspace and to avoid races with lmkd by
reclaiming apps as soon as they entered the cached state. Additionally,
it could provide many chances for platform to use much information to
optimize memory efficiency.
To achieve the goal, the patchset introduce two new options for madvise.
One is MADV_COLD which will deactivate activated pages and the other is
MADV_PAGEOUT which will reclaim private pages instantly. These new
options complement MADV_DONTNEED and MADV_FREE by adding non-destructive
ways to gain some free memory space. MADV_PAGEOUT is similar to
MADV_DONTNEED in a way that it hints the kernel that memory region is not
currently needed and should be reclaimed immediately; MADV_COLD is similar
to MADV_FREE in a way that it hints the kernel that memory region is not
currently needed and should be reclaimed when memory pressure rises.
This patch (of 5):
When a process expects no accesses to a certain memory range, it could
give a hint to kernel that the pages can be reclaimed when memory pressure
happens but data should be preserved for future use. This could reduce
workingset eviction so it ends up increasing performance.
This patch introduces the new MADV_COLD hint to madvise(2) syscall.
MADV_COLD can be used by a process to mark a memory range as not expected
to be used in the near future. The hint can help kernel in deciding which
pages to evict early during memory pressure.
It works for every LRU pages like MADV_[DONTNEED|FREE]. IOW, It moves
active file page -> inactive file LRU
active anon page -> inacdtive anon LRU
Unlike MADV_FREE, it doesn't move active anonymous pages to inactive file
LRU's head because MADV_COLD is a little bit different symantic.
MADV_FREE means it's okay to discard when the memory pressure because the
content of the page is *garbage* so freeing such pages is almost zero
overhead since we don't need to swap out and access afterward causes just
minor fault. Thus, it would make sense to put those freeable pages in
inactive file LRU to compete other used-once pages. It makes sense for
implmentaion point of view, too because it's not swapbacked memory any
longer until it would be re-dirtied. Even, it could give a bonus to make
them be reclaimed on swapless system. However, MADV_COLD doesn't mean
garbage so reclaiming them requires swap-out/in in the end so it's bigger
cost. Since we have designed VM LRU aging based on cost-model, anonymous
cold pages would be better to position inactive anon's LRU list, not file
LRU. Furthermore, it would help to avoid unnecessary scanning if system
doesn't have a swap device. Let's start simpler way without adding
complexity at this moment. However, keep in mind, too that it's a caveat
that workloads with a lot of pages cache are likely to ignore MADV_COLD on
anonymous memory because we rarely age anonymous LRU lists.
* man-page material
MADV_COLD (since Linux x.x)
Pages in the specified regions will be treated as less-recently-accessed
compared to pages in the system with similar access frequencies. In
contrast to MADV_FREE, the contents of the region are preserved regardless
of subsequent writes to pages.
MADV_COLD cannot be applied to locked pages, Huge TLB pages, or VM_PFNMAP
pages.
[akpm@linux-foundation.org: resolve conflicts with hmm.git]
Link: http://lkml.kernel.org/r/20190726023435.214162-2-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
Reported-by: kbuild test robot <lkp@intel.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: James E.J. Bottomley <James.Bottomley@HansenPartnership.com>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Chris Zankel <chris@zankel.net>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Daniel Colascione <dancol@google.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Hillf Danton <hdanton@sina.com>
Cc: Joel Fernandes (Google) <joel@joelfernandes.org>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Oleksandr Natalenko <oleksandr@redhat.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Sonny Rao <sonnyrao@google.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Tim Murray <timmurray@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-09-25 16:49:08 -07:00
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mm/madvise: introduce MADV_POPULATE_(READ|WRITE) to prefault page tables
I. Background: Sparse Memory Mappings
When we manage sparse memory mappings dynamically in user space - also
sometimes involving MAP_NORESERVE - we want to dynamically populate/
discard memory inside such a sparse memory region. Example users are
hypervisors (especially implementing memory ballooning or similar
technologies like virtio-mem) and memory allocators. In addition, we want
to fail in a nice way (instead of generating SIGBUS) if populating does
not succeed because we are out of backend memory (which can happen easily
with file-based mappings, especially tmpfs and hugetlbfs).
While MADV_DONTNEED, MADV_REMOVE and FALLOC_FL_PUNCH_HOLE allow for
reliably discarding memory for most mapping types, there is no generic
approach to populate page tables and preallocate memory.
Although mmap() supports MAP_POPULATE, it is not applicable to the concept
of sparse memory mappings, where we want to populate/discard dynamically
and avoid expensive/problematic remappings. In addition, we never
actually report errors during the final populate phase - it is best-effort
only.
fallocate() can be used to preallocate file-based memory and fail in a
safe way. However, it cannot really be used for any private mappings on
anonymous files via memfd due to COW semantics. In addition, fallocate()
does not actually populate page tables, so we still always get pagefaults
on first access - which is sometimes undesired (i.e., real-time workloads)
and requires real prefaulting of page tables, not just a preallocation of
backend storage. There might be interesting use cases for sparse memory
regions along with mlockall(MCL_ONFAULT) which fallocate() cannot satisfy
as it does not prefault page tables.
II. On preallcoation/prefaulting from user space
Because we don't have a proper interface, what applications (like QEMU and
databases) end up doing is touching (i.e., reading+writing one byte to not
overwrite existing data) all individual pages.
However, that approach
1) Can result in wear on storage backing, because we end up reading/writing
each page; this is especially a problem for dax/pmem.
2) Can result in mmap_sem contention when prefaulting via multiple
threads.
3) Requires expensive signal handling, especially to catch SIGBUS in case
of hugetlbfs/shmem/file-backed memory. For example, this is
problematic in hypervisors like QEMU where SIGBUS handlers might already
be used by other subsystems concurrently to e.g, handle hardware errors.
"Simply" doing preallocation concurrently from other thread is not that
easy.
III. On MADV_WILLNEED
Extending MADV_WILLNEED is not an option because
1. It would change the semantics: "Expect access in the near future." and
"might be a good idea to read some pages" vs. "Definitely populate/
preallocate all memory and definitely fail on errors.".
2. Existing users (like virtio-balloon in QEMU when deflating the balloon)
don't want populate/prealloc semantics. They treat this rather as a hint
to give a little performance boost without too much overhead - and don't
expect that a lot of memory might get consumed or a lot of time
might be spent.
IV. MADV_POPULATE_READ and MADV_POPULATE_WRITE
Let's introduce MADV_POPULATE_READ and MADV_POPULATE_WRITE, inspired by
MAP_POPULATE, with the following semantics:
1. MADV_POPULATE_READ can be used to prefault page tables just like
manually reading each individual page. This will not break any COW
mappings. The shared zero page might get mapped and no backend storage
might get preallocated -- allocation might be deferred to
write-fault time. Especially shared file mappings require an explicit
fallocate() upfront to actually preallocate backend memory (blocks in
the file system) in case the file might have holes.
2. If MADV_POPULATE_READ succeeds, all page tables have been populated
(prefaulted) readable once.
3. MADV_POPULATE_WRITE can be used to preallocate backend memory and
prefault page tables just like manually writing (or
reading+writing) each individual page. This will break any COW
mappings -- e.g., the shared zeropage is never populated.
4. If MADV_POPULATE_WRITE succeeds, all page tables have been populated
(prefaulted) writable once.
5. MADV_POPULATE_READ and MADV_POPULATE_WRITE cannot be applied to special
mappings marked with VM_PFNMAP and VM_IO. Also, proper access
permissions (e.g., PROT_READ, PROT_WRITE) are required. If any such
mapping is encountered, madvise() fails with -EINVAL.
6. If MADV_POPULATE_READ or MADV_POPULATE_WRITE fails, some page tables
might have been populated.
7. MADV_POPULATE_READ and MADV_POPULATE_WRITE will return -EHWPOISON
when encountering a HW poisoned page in the range.
8. Similar to MAP_POPULATE, MADV_POPULATE_READ and MADV_POPULATE_WRITE
cannot protect from the OOM (Out Of Memory) handler killing the
process.
While the use case for MADV_POPULATE_WRITE is fairly obvious (i.e.,
preallocate memory and prefault page tables for VMs), one issue is that
whenever we prefault pages writable, the pages have to be marked dirty,
because the CPU could dirty them any time. while not a real problem for
hugetlbfs or dax/pmem, it can be a problem for shared file mappings: each
page will be marked dirty and has to be written back later when evicting.
MADV_POPULATE_READ allows for optimizing this scenario: Pre-read a whole
mapping from backend storage without marking it dirty, such that eviction
won't have to write it back. As discussed above, shared file mappings
might require an explciit fallocate() upfront to achieve
preallcoation+prepopulation.
Although sparse memory mappings are the primary use case, this will also
be useful for other preallocate/prefault use cases where MAP_POPULATE is
not desired or the semantics of MAP_POPULATE are not sufficient: as one
example, QEMU users can trigger preallocation/prefaulting of guest RAM
after the mapping was created -- and don't want errors to be silently
suppressed.
Looking at the history, MADV_POPULATE was already proposed in 2013 [1],
however, the main motivation back than was performance improvements --
which should also still be the case.
V. Single-threaded performance comparison
I did a short experiment, prefaulting page tables on completely *empty
mappings/files* and repeated the experiment 10 times. The results
correspond to the shortest execution time. In general, the performance
benefit for huge pages is negligible with small mappings.
V.1: Private mappings
POPULATE_READ and POPULATE_WRITE is fastest. Note that
Reading/POPULATE_READ will populate the shared zeropage where applicable
-- which result in short population times.
The fastest way to allocate backend storage (here: swap or huge pages) and
prefault page tables is POPULATE_WRITE.
V.2: Shared mappings
fallocate() is fastest, however, doesn't prefault page tables.
POPULATE_WRITE is faster than simple writes and read/writes.
POPULATE_READ is faster than simple reads.
Without a fd, the fastest way to allocate backend storage and prefault
page tables is POPULATE_WRITE. With an fd, the fastest way is usually
FALLOCATE+POPULATE_READ or FALLOCATE+POPULATE_WRITE respectively; one
exception are actual files: FALLOCATE+Read is slightly faster than
FALLOCATE+POPULATE_READ.
The fastest way to allocate backend storage prefault page tables is
FALLOCATE+POPULATE_WRITE -- except when dealing with actual files; then,
FALLOCATE+POPULATE_READ is fastest and won't directly mark all pages as
dirty.
v.3: Detailed results
==================================================
2 MiB MAP_PRIVATE:
**************************************************
Anon 4 KiB : Read : 0.119 ms
Anon 4 KiB : Write : 0.222 ms
Anon 4 KiB : Read/Write : 0.380 ms
Anon 4 KiB : POPULATE_READ : 0.060 ms
Anon 4 KiB : POPULATE_WRITE : 0.158 ms
Memfd 4 KiB : Read : 0.034 ms
Memfd 4 KiB : Write : 0.310 ms
Memfd 4 KiB : Read/Write : 0.362 ms
Memfd 4 KiB : POPULATE_READ : 0.039 ms
Memfd 4 KiB : POPULATE_WRITE : 0.229 ms
Memfd 2 MiB : Read : 0.030 ms
Memfd 2 MiB : Write : 0.030 ms
Memfd 2 MiB : Read/Write : 0.030 ms
Memfd 2 MiB : POPULATE_READ : 0.030 ms
Memfd 2 MiB : POPULATE_WRITE : 0.030 ms
tmpfs : Read : 0.033 ms
tmpfs : Write : 0.313 ms
tmpfs : Read/Write : 0.406 ms
tmpfs : POPULATE_READ : 0.039 ms
tmpfs : POPULATE_WRITE : 0.285 ms
file : Read : 0.033 ms
file : Write : 0.351 ms
file : Read/Write : 0.408 ms
file : POPULATE_READ : 0.039 ms
file : POPULATE_WRITE : 0.290 ms
hugetlbfs : Read : 0.030 ms
hugetlbfs : Write : 0.030 ms
hugetlbfs : Read/Write : 0.030 ms
hugetlbfs : POPULATE_READ : 0.030 ms
hugetlbfs : POPULATE_WRITE : 0.030 ms
**************************************************
4096 MiB MAP_PRIVATE:
**************************************************
Anon 4 KiB : Read : 237.940 ms
Anon 4 KiB : Write : 708.409 ms
Anon 4 KiB : Read/Write : 1054.041 ms
Anon 4 KiB : POPULATE_READ : 124.310 ms
Anon 4 KiB : POPULATE_WRITE : 572.582 ms
Memfd 4 KiB : Read : 136.928 ms
Memfd 4 KiB : Write : 963.898 ms
Memfd 4 KiB : Read/Write : 1106.561 ms
Memfd 4 KiB : POPULATE_READ : 78.450 ms
Memfd 4 KiB : POPULATE_WRITE : 805.881 ms
Memfd 2 MiB : Read : 357.116 ms
Memfd 2 MiB : Write : 357.210 ms
Memfd 2 MiB : Read/Write : 357.606 ms
Memfd 2 MiB : POPULATE_READ : 356.094 ms
Memfd 2 MiB : POPULATE_WRITE : 356.937 ms
tmpfs : Read : 137.536 ms
tmpfs : Write : 954.362 ms
tmpfs : Read/Write : 1105.954 ms
tmpfs : POPULATE_READ : 80.289 ms
tmpfs : POPULATE_WRITE : 822.826 ms
file : Read : 137.874 ms
file : Write : 987.025 ms
file : Read/Write : 1107.439 ms
file : POPULATE_READ : 80.413 ms
file : POPULATE_WRITE : 857.622 ms
hugetlbfs : Read : 355.607 ms
hugetlbfs : Write : 355.729 ms
hugetlbfs : Read/Write : 356.127 ms
hugetlbfs : POPULATE_READ : 354.585 ms
hugetlbfs : POPULATE_WRITE : 355.138 ms
**************************************************
2 MiB MAP_SHARED:
**************************************************
Anon 4 KiB : Read : 0.394 ms
Anon 4 KiB : Write : 0.348 ms
Anon 4 KiB : Read/Write : 0.400 ms
Anon 4 KiB : POPULATE_READ : 0.326 ms
Anon 4 KiB : POPULATE_WRITE : 0.273 ms
Anon 2 MiB : Read : 0.030 ms
Anon 2 MiB : Write : 0.030 ms
Anon 2 MiB : Read/Write : 0.030 ms
Anon 2 MiB : POPULATE_READ : 0.030 ms
Anon 2 MiB : POPULATE_WRITE : 0.030 ms
Memfd 4 KiB : Read : 0.412 ms
Memfd 4 KiB : Write : 0.372 ms
Memfd 4 KiB : Read/Write : 0.419 ms
Memfd 4 KiB : POPULATE_READ : 0.343 ms
Memfd 4 KiB : POPULATE_WRITE : 0.288 ms
Memfd 4 KiB : FALLOCATE : 0.137 ms
Memfd 4 KiB : FALLOCATE+Read : 0.446 ms
Memfd 4 KiB : FALLOCATE+Write : 0.330 ms
Memfd 4 KiB : FALLOCATE+Read/Write : 0.454 ms
Memfd 4 KiB : FALLOCATE+POPULATE_READ : 0.379 ms
Memfd 4 KiB : FALLOCATE+POPULATE_WRITE : 0.268 ms
Memfd 2 MiB : Read : 0.030 ms
Memfd 2 MiB : Write : 0.030 ms
Memfd 2 MiB : Read/Write : 0.030 ms
Memfd 2 MiB : POPULATE_READ : 0.030 ms
Memfd 2 MiB : POPULATE_WRITE : 0.030 ms
Memfd 2 MiB : FALLOCATE : 0.030 ms
Memfd 2 MiB : FALLOCATE+Read : 0.031 ms
Memfd 2 MiB : FALLOCATE+Write : 0.031 ms
Memfd 2 MiB : FALLOCATE+Read/Write : 0.031 ms
Memfd 2 MiB : FALLOCATE+POPULATE_READ : 0.030 ms
Memfd 2 MiB : FALLOCATE+POPULATE_WRITE : 0.030 ms
tmpfs : Read : 0.416 ms
tmpfs : Write : 0.369 ms
tmpfs : Read/Write : 0.425 ms
tmpfs : POPULATE_READ : 0.346 ms
tmpfs : POPULATE_WRITE : 0.295 ms
tmpfs : FALLOCATE : 0.139 ms
tmpfs : FALLOCATE+Read : 0.447 ms
tmpfs : FALLOCATE+Write : 0.333 ms
tmpfs : FALLOCATE+Read/Write : 0.454 ms
tmpfs : FALLOCATE+POPULATE_READ : 0.380 ms
tmpfs : FALLOCATE+POPULATE_WRITE : 0.272 ms
file : Read : 0.191 ms
file : Write : 0.511 ms
file : Read/Write : 0.524 ms
file : POPULATE_READ : 0.196 ms
file : POPULATE_WRITE : 0.434 ms
file : FALLOCATE : 0.004 ms
file : FALLOCATE+Read : 0.197 ms
file : FALLOCATE+Write : 0.554 ms
file : FALLOCATE+Read/Write : 0.480 ms
file : FALLOCATE+POPULATE_READ : 0.201 ms
file : FALLOCATE+POPULATE_WRITE : 0.381 ms
hugetlbfs : Read : 0.030 ms
hugetlbfs : Write : 0.030 ms
hugetlbfs : Read/Write : 0.030 ms
hugetlbfs : POPULATE_READ : 0.030 ms
hugetlbfs : POPULATE_WRITE : 0.030 ms
hugetlbfs : FALLOCATE : 0.030 ms
hugetlbfs : FALLOCATE+Read : 0.031 ms
hugetlbfs : FALLOCATE+Write : 0.031 ms
hugetlbfs : FALLOCATE+Read/Write : 0.030 ms
hugetlbfs : FALLOCATE+POPULATE_READ : 0.030 ms
hugetlbfs : FALLOCATE+POPULATE_WRITE : 0.030 ms
**************************************************
4096 MiB MAP_SHARED:
**************************************************
Anon 4 KiB : Read : 1053.090 ms
Anon 4 KiB : Write : 913.642 ms
Anon 4 KiB : Read/Write : 1060.350 ms
Anon 4 KiB : POPULATE_READ : 893.691 ms
Anon 4 KiB : POPULATE_WRITE : 782.885 ms
Anon 2 MiB : Read : 358.553 ms
Anon 2 MiB : Write : 358.419 ms
Anon 2 MiB : Read/Write : 357.992 ms
Anon 2 MiB : POPULATE_READ : 357.533 ms
Anon 2 MiB : POPULATE_WRITE : 357.808 ms
Memfd 4 KiB : Read : 1078.144 ms
Memfd 4 KiB : Write : 942.036 ms
Memfd 4 KiB : Read/Write : 1100.391 ms
Memfd 4 KiB : POPULATE_READ : 925.829 ms
Memfd 4 KiB : POPULATE_WRITE : 804.394 ms
Memfd 4 KiB : FALLOCATE : 304.632 ms
Memfd 4 KiB : FALLOCATE+Read : 1163.359 ms
Memfd 4 KiB : FALLOCATE+Write : 933.186 ms
Memfd 4 KiB : FALLOCATE+Read/Write : 1187.304 ms
Memfd 4 KiB : FALLOCATE+POPULATE_READ : 1013.660 ms
Memfd 4 KiB : FALLOCATE+POPULATE_WRITE : 794.560 ms
Memfd 2 MiB : Read : 358.131 ms
Memfd 2 MiB : Write : 358.099 ms
Memfd 2 MiB : Read/Write : 358.250 ms
Memfd 2 MiB : POPULATE_READ : 357.563 ms
Memfd 2 MiB : POPULATE_WRITE : 357.334 ms
Memfd 2 MiB : FALLOCATE : 356.735 ms
Memfd 2 MiB : FALLOCATE+Read : 358.152 ms
Memfd 2 MiB : FALLOCATE+Write : 358.331 ms
Memfd 2 MiB : FALLOCATE+Read/Write : 358.018 ms
Memfd 2 MiB : FALLOCATE+POPULATE_READ : 357.286 ms
Memfd 2 MiB : FALLOCATE+POPULATE_WRITE : 357.523 ms
tmpfs : Read : 1087.265 ms
tmpfs : Write : 950.840 ms
tmpfs : Read/Write : 1107.567 ms
tmpfs : POPULATE_READ : 922.605 ms
tmpfs : POPULATE_WRITE : 810.094 ms
tmpfs : FALLOCATE : 306.320 ms
tmpfs : FALLOCATE+Read : 1169.796 ms
tmpfs : FALLOCATE+Write : 933.730 ms
tmpfs : FALLOCATE+Read/Write : 1191.610 ms
tmpfs : FALLOCATE+POPULATE_READ : 1020.474 ms
tmpfs : FALLOCATE+POPULATE_WRITE : 798.945 ms
file : Read : 654.101 ms
file : Write : 1259.142 ms
file : Read/Write : 1289.509 ms
file : POPULATE_READ : 661.642 ms
file : POPULATE_WRITE : 1106.816 ms
file : FALLOCATE : 1.864 ms
file : FALLOCATE+Read : 656.328 ms
file : FALLOCATE+Write : 1153.300 ms
file : FALLOCATE+Read/Write : 1180.613 ms
file : FALLOCATE+POPULATE_READ : 668.347 ms
file : FALLOCATE+POPULATE_WRITE : 996.143 ms
hugetlbfs : Read : 357.245 ms
hugetlbfs : Write : 357.413 ms
hugetlbfs : Read/Write : 357.120 ms
hugetlbfs : POPULATE_READ : 356.321 ms
hugetlbfs : POPULATE_WRITE : 356.693 ms
hugetlbfs : FALLOCATE : 355.927 ms
hugetlbfs : FALLOCATE+Read : 357.074 ms
hugetlbfs : FALLOCATE+Write : 357.120 ms
hugetlbfs : FALLOCATE+Read/Write : 356.983 ms
hugetlbfs : FALLOCATE+POPULATE_READ : 356.413 ms
hugetlbfs : FALLOCATE+POPULATE_WRITE : 356.266 ms
**************************************************
[1] https://lkml.org/lkml/2013/6/27/698
[akpm@linux-foundation.org: coding style fixes]
Link: https://lkml.kernel.org/r/20210419135443.12822-3-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>
Cc: Helge Deller <deller@gmx.de>
Cc: Chris Zankel <chris@zankel.net>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rolf Eike Beer <eike-kernel@sf-tec.de>
Cc: Ram Pai <linuxram@us.ibm.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-06-30 18:52:28 -07:00
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#define MADV_POPULATE_READ 22 /* populate (prefault) page tables readable */
|
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|
|
#define MADV_POPULATE_WRITE 23 /* populate (prefault) page tables writable */
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|
mm: madvise: MADV_DONTNEED_LOCKED
MADV_DONTNEED historically rejects mlocked ranges, but with MLOCK_ONFAULT
and MCL_ONFAULT allowing to mlock without populating, there are valid use
cases for depopulating locked ranges as well.
Users mlock memory to protect secrets. There are allocators for secure
buffers that want in-use memory generally mlocked, but cleared and
invalidated memory to give up the physical pages. This could be done with
explicit munlock -> mlock calls on free -> alloc of course, but that adds
two unnecessary syscalls, heavy mmap_sem write locks, vma splits and
re-merges - only to get rid of the backing pages.
Users also mlockall(MCL_ONFAULT) to suppress sustained paging, but are
okay with on-demand initial population. It seems valid to selectively
free some memory during the lifetime of such a process, without having to
mess with its overall policy.
Why add a separate flag? Isn't this a pretty niche usecase?
- MADV_DONTNEED has been bailing on locked vmas forever. It's at least
conceivable that someone, somewhere is relying on mlock to protect
data from perhaps broader invalidation calls. Changing this behavior
now could lead to quiet data corruption.
- It also clarifies expectations around MADV_FREE and maybe
MADV_REMOVE. It avoids the situation where one quietly behaves
different than the others. MADV_FREE_LOCKED can be added later.
- The combination of mlock() and madvise() in the first place is
probably niche. But where it happens, I'd say that dropping pages
from a locked region once they don't contain secrets or won't page
anymore is much saner than relying on mlock to protect memory from
speculative or errant invalidation calls. It's just that we can't
change the default behavior because of the two previous points.
Given that, an explicit new flag seems to make the most sense.
[hannes@cmpxchg.org: fix mips build]
Link: https://lkml.kernel.org/r/20220304171912.305060-1-hannes@cmpxchg.org
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Nadav Amit <nadav.amit@gmail.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2022-03-24 18:14:12 -07:00
|
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#define MADV_DONTNEED_LOCKED 24 /* like DONTNEED, but drop locked pages too */
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mm/madvise: introduce MADV_COLLAPSE sync hugepage collapse
This idea was introduced by David Rientjes[1].
Introduce a new madvise mode, MADV_COLLAPSE, that allows users to request
a synchronous collapse of memory at their own expense.
The benefits of this approach are:
* CPU is charged to the process that wants to spend the cycles for the
THP
* Avoid unpredictable timing of khugepaged collapse
Semantics
This call is independent of the system-wide THP sysfs settings, but will
fail for memory marked VM_NOHUGEPAGE. If the ranges provided span
multiple VMAs, the semantics of the collapse over each VMA is independent
from the others. This implies a hugepage cannot cross a VMA boundary. If
collapse of a given hugepage-aligned/sized region fails, the operation may
continue to attempt collapsing the remainder of memory specified.
The memory ranges provided must be page-aligned, but are not required to
be hugepage-aligned. If the memory ranges are not hugepage-aligned, the
start/end of the range will be clamped to the first/last hugepage-aligned
address covered by said range. The memory ranges must span at least one
hugepage-sized region.
All non-resident pages covered by the range will first be
swapped/faulted-in, before being internally copied onto a freshly
allocated hugepage. Unmapped pages will have their data directly
initialized to 0 in the new hugepage. However, for every eligible
hugepage aligned/sized region to-be collapsed, at least one page must
currently be backed by memory (a PMD covering the address range must
already exist).
Allocation for the new hugepage may enter direct reclaim and/or
compaction, regardless of VMA flags. When the system has multiple NUMA
nodes, the hugepage will be allocated from the node providing the most
native pages. This operation operates on the current state of the
specified process and makes no persistent changes or guarantees on how
pages will be mapped, constructed, or faulted in the future
Return Value
If all hugepage-sized/aligned regions covered by the provided range were
either successfully collapsed, or were already PMD-mapped THPs, this
operation will be deemed successful. On success, process_madvise(2)
returns the number of bytes advised, and madvise(2) returns 0. Else, -1
is returned and errno is set to indicate the error for the most-recently
attempted hugepage collapse. Note that many failures might have occurred,
since the operation may continue to collapse in the event a single
hugepage-sized/aligned region fails.
ENOMEM Memory allocation failed or VMA not found
EBUSY Memcg charging failed
EAGAIN Required resource temporarily unavailable. Try again
might succeed.
EINVAL Other error: No PMD found, subpage doesn't have Present
bit set, "Special" page no backed by struct page, VMA
incorrectly sized, address not page-aligned, ...
Most notable here is ENOMEM and EBUSY (new to madvise) which are intended
to provide the caller with actionable feedback so they may take an
appropriate fallback measure.
Use Cases
An immediate user of this new functionality are malloc() implementations
that manage memory in hugepage-sized chunks, but sometimes subrelease
memory back to the system in native-sized chunks via MADV_DONTNEED;
zapping the pmd. Later, when the memory is hot, the implementation could
madvise(MADV_COLLAPSE) to re-back the memory by THPs to regain hugepage
coverage and dTLB performance. TCMalloc is such an implementation that
could benefit from this[2].
Only privately-mapped anon memory is supported for now, but additional
support for file, shmem, and HugeTLB high-granularity mappings[2] is
expected. File and tmpfs/shmem support would permit:
* Backing executable text by THPs. Current support provided by
CONFIG_READ_ONLY_THP_FOR_FS may take a long time on a large system which
might impair services from serving at their full rated load after
(re)starting. Tricks like mremap(2)'ing text onto anonymous memory to
immediately realize iTLB performance prevents page sharing and demand
paging, both of which increase steady state memory footprint. With
MADV_COLLAPSE, we get the best of both worlds: Peak upfront performance
and lower RAM footprints.
* Backing guest memory by hugapages after the memory contents have been
migrated in native-page-sized chunks to a new host, in a
userfaultfd-based live-migration stack.
[1] https://lore.kernel.org/linux-mm/d098c392-273a-36a4-1a29-59731cdf5d3d@google.com/
[2] https://github.com/google/tcmalloc/tree/master/tcmalloc
[jrdr.linux@gmail.com: avoid possible memory leak in failure path]
Link: https://lkml.kernel.org/r/20220713024109.62810-1-jrdr.linux@gmail.com
[zokeefe@google.com add missing kfree() to madvise_collapse()]
Link: https://lore.kernel.org/linux-mm/20220713024109.62810-1-jrdr.linux@gmail.com/
Link: https://lkml.kernel.org/r/20220713161851.1879439-1-zokeefe@google.com
[zokeefe@google.com: delay computation of hpage boundaries until use]]
Link: https://lkml.kernel.org/r/20220720140603.1958773-4-zokeefe@google.com
Link: https://lkml.kernel.org/r/20220706235936.2197195-10-zokeefe@google.com
Signed-off-by: Zach O'Keefe <zokeefe@google.com>
Signed-off-by: "Souptick Joarder (HPE)" <jrdr.linux@gmail.com>
Suggested-by: David Rientjes <rientjes@google.com>
Cc: Alex Shi <alex.shi@linux.alibaba.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Chris Kennelly <ckennelly@google.com>
Cc: Chris Zankel <chris@zankel.net>
Cc: David Hildenbrand <david@redhat.com>
Cc: Helge Deller <deller@gmx.de>
Cc: Hugh Dickins <hughd@google.com>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Pavel Begunkov <asml.silence@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rongwei Wang <rongwei.wang@linux.alibaba.com>
Cc: SeongJae Park <sj@kernel.org>
Cc: Song Liu <songliubraving@fb.com>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-07-06 16:59:27 -07:00
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#define MADV_COLLAPSE 25 /* Synchronous hugepage collapse */
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mm: madvise: implement lightweight guard page mechanism
Implement a new lightweight guard page feature, that is regions of
userland virtual memory that, when accessed, cause a fatal signal to
arise.
Currently users must establish PROT_NONE ranges to achieve this.
However this is very costly memory-wise - we need a VMA for each and every
one of these regions AND they become unmergeable with surrounding VMAs.
In addition repeated mmap() calls require repeated kernel context switches
and contention of the mmap lock to install these ranges, potentially also
having to unmap memory if installed over existing ranges.
The lightweight guard approach eliminates the VMA cost altogether - rather
than establishing a PROT_NONE VMA, it operates at the level of page table
entries - establishing PTE markers such that accesses to them cause a
fault followed by a SIGSGEV signal being raised.
This is achieved through the PTE marker mechanism, which we have already
extended to provide PTE_MARKER_GUARD, which we installed via the generic
page walking logic which we have extended for this purpose.
These guard ranges are established with MADV_GUARD_INSTALL. If the range
in which they are installed contain any existing mappings, they will be
zapped, i.e. free the range and unmap memory (thus mimicking the
behaviour of MADV_DONTNEED in this respect).
Any existing guard entries will be left untouched. There is therefore no
nesting of guarded pages.
Guarded ranges are NOT cleared by MADV_DONTNEED nor MADV_FREE (in both
instances the memory range may be reused at which point a user would
expect guards to still be in place), but they are cleared via
MADV_GUARD_REMOVE, process teardown or unmapping of memory ranges.
The guard property can be removed from ranges via MADV_GUARD_REMOVE. The
ranges over which this is applied, should they contain non-guard entries,
will be untouched, with only guard entries being cleared.
We permit this operation on anonymous memory only, and only VMAs which are
non-special, non-huge and not mlock()'d (if we permitted this we'd have to
drop locked pages which would be rather counterintuitive).
Racing page faults can cause repeated attempts to install guard pages that
are interrupted, result in a zap, and this process can end up being
repeated. If this happens more than would be expected in normal
operation, we rescind locks and retry the whole thing, which avoids lock
contention in this scenario.
Link: https://lkml.kernel.org/r/6aafb5821bf209f277dfae0787abb2ef87a37542.1730123433.git.lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Suggested-by: Vlastimil Babka <vbabka@suse.cz>
Suggested-by: Jann Horn <jannh@google.com>
Suggested-by: David Hildenbrand <david@redhat.com>
Suggested-by: Vlastimil Babka <vbabka@suse.cz>
Suggested-by: Jann Horn <jannh@google.com>
Suggested-by: David Hildenbrand <david@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Arnd Bergmann <arnd@kernel.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Chris Zankel <chris@zankel.net>
Cc: Helge Deller <deller@gmx.de>
Cc: James E.J. Bottomley <James.Bottomley@HansenPartnership.com>
Cc: Jeff Xu <jeffxu@chromium.org>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Liam R. Howlett <Liam.Howlett@Oracle.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Richard Henderson <richard.henderson@linaro.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2024-10-28 14:13:29 +00:00
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#define MADV_GUARD_INSTALL 102 /* fatal signal on access to range */
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#define MADV_GUARD_REMOVE 103 /* unguard range */
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2006-02-15 15:17:39 -08:00
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/* compatibility flags */
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#define MAP_FILE 0
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x86/pkeys: Allocation/free syscalls
This patch adds two new system calls:
int pkey_alloc(unsigned long flags, unsigned long init_access_rights)
int pkey_free(int pkey);
These implement an "allocator" for the protection keys
themselves, which can be thought of as analogous to the allocator
that the kernel has for file descriptors. The kernel tracks
which numbers are in use, and only allows operations on keys that
are valid. A key which was not obtained by pkey_alloc() may not,
for instance, be passed to pkey_mprotect().
These system calls are also very important given the kernel's use
of pkeys to implement execute-only support. These help ensure
that userspace can never assume that it has control of a key
unless it first asks the kernel. The kernel does not promise to
preserve PKRU (right register) contents except for allocated
pkeys.
The 'init_access_rights' argument to pkey_alloc() specifies the
rights that will be established for the returned pkey. For
instance:
pkey = pkey_alloc(flags, PKEY_DENY_WRITE);
will allocate 'pkey', but also sets the bits in PKRU[1] such that
writing to 'pkey' is already denied.
The kernel does not prevent pkey_free() from successfully freeing
in-use pkeys (those still assigned to a memory range by
pkey_mprotect()). It would be expensive to implement the checks
for this, so we instead say, "Just don't do it" since sane
software will never do it anyway.
Any piece of userspace calling pkey_alloc() needs to be prepared
for it to fail. Why? pkey_alloc() returns the same error code
(ENOSPC) when there are no pkeys and when pkeys are unsupported.
They can be unsupported for a whole host of reasons, so apps must
be prepared for this. Also, libraries or LD_PRELOADs might steal
keys before an application gets access to them.
This allocation mechanism could be implemented in userspace.
Even if we did it in userspace, we would still need additional
user/kernel interfaces to tell userspace which keys are being
used by the kernel internally (such as for execute-only
mappings). Having the kernel provide this facility completely
removes the need for these additional interfaces, or having an
implementation of this in userspace at all.
Note that we have to make changes to all of the architectures
that do not use mman-common.h because we use the new
PKEY_DENY_ACCESS/WRITE macros in arch-independent code.
1. PKRU is the Protection Key Rights User register. It is a
usermode-accessible register that controls whether writes
and/or access to each individual pkey is allowed or denied.
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Cc: linux-arch@vger.kernel.org
Cc: Dave Hansen <dave@sr71.net>
Cc: arnd@arndb.de
Cc: linux-api@vger.kernel.org
Cc: linux-mm@kvack.org
Cc: luto@kernel.org
Cc: akpm@linux-foundation.org
Cc: torvalds@linux-foundation.org
Link: http://lkml.kernel.org/r/20160729163015.444FE75F@viggo.jf.intel.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2016-07-29 09:30:15 -07:00
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#define PKEY_DISABLE_ACCESS 0x1
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#define PKEY_DISABLE_WRITE 0x2
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#define PKEY_ACCESS_MASK (PKEY_DISABLE_ACCESS |\
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PKEY_DISABLE_WRITE)
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2009-05-13 22:56:24 +00:00
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#endif /* __ASM_GENERIC_MMAN_COMMON_H */
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