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userfaultfd: move userfaultfd_ctx struct to header file

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Patch series "per-vma locks in userfaultfd", v7.

Performing userfaultfd operations (like copy/move etc.) in critical
section of mmap_lock (read-mode) causes significant contention on the lock
when operations requiring the lock in write-mode are taking place
concurrently.  We can use per-vma locks instead to significantly reduce
the contention issue.

Android runtime's Garbage Collector uses userfaultfd for concurrent
compaction.  mmap-lock contention during compaction potentially causes
jittery experience for the user.  During one such reproducible scenario,
we observed the following improvements with this patch-set:

- Wall clock time of compaction phase came down from ~3s to <500ms
- Uninterruptible sleep time (across all threads in the process) was
  ~10ms (none in mmap_lock) during compaction, instead of >20s


This patch (of 4):

Move the struct to userfaultfd_k.h to be accessible from mm/userfaultfd.c.
There are no other changes in the struct.

This is required to prepare for using per-vma locks in userfaultfd
operations.

Link: https://lkml.kernel.org/r/20240215182756.3448972-1-lokeshgidra@google.com
Link: https://lkml.kernel.org/r/20240215182756.3448972-2-lokeshgidra@google.com
Signed-off-by: Lokesh Gidra <lokeshgidra@google.com>
Reviewed-by: Mike Rapoport (IBM) <rppt@kernel.org>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Brian Geffon <bgeffon@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: Kalesh Singh <kaleshsingh@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Nicolas Geoffray <ngeoffray@google.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Tim Murray <timmurray@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Lokesh Gidra 2024-02-15 10:27:53 -08:00 committed by Andrew Morton
parent 952237b5a9
commit f91e6b41dd
2 changed files with 39 additions and 39 deletions
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39
fs/userfaultfd.c
View File

@ -50,45 +50,6 @@ static struct ctl_table vm_userfaultfd_table[] = {
static struct kmem_cache *userfaultfd_ctx_cachep __ro_after_init;
/*
* Start with fault_pending_wqh and fault_wqh so they're more likely
* to be in the same cacheline.
*
* Locking order:
* fd_wqh.lock
* fault_pending_wqh.lock
* fault_wqh.lock
* event_wqh.lock
*
* To avoid deadlocks, IRQs must be disabled when taking any of the above locks,
* since fd_wqh.lock is taken by aio_poll() while it's holding a lock that's
* also taken in IRQ context.
*/
struct userfaultfd_ctx {
/* waitqueue head for the pending (i.e. not read) userfaults */
wait_queue_head_t fault_pending_wqh;
/* waitqueue head for the userfaults */
wait_queue_head_t fault_wqh;
/* waitqueue head for the pseudo fd to wakeup poll/read */
wait_queue_head_t fd_wqh;
/* waitqueue head for events */
wait_queue_head_t event_wqh;
/* a refile sequence protected by fault_pending_wqh lock */
seqcount_spinlock_t refile_seq;
/* pseudo fd refcounting */
refcount_t refcount;
/* userfaultfd syscall flags */
unsigned int flags;
/* features requested from the userspace */
unsigned int features;
/* released */
bool released;
/* memory mappings are changing because of non-cooperative event */
atomic_t mmap_changing;
/* mm with one ore more vmas attached to this userfaultfd_ctx */
struct mm_struct *mm;
};
struct userfaultfd_fork_ctx {
struct userfaultfd_ctx *orig;
struct userfaultfd_ctx *new;

39
include/linux/userfaultfd_k.h
View File

@ -36,6 +36,45 @@
#define UFFD_SHARED_FCNTL_FLAGS (O_CLOEXEC | O_NONBLOCK)
#define UFFD_FLAGS_SET (EFD_SHARED_FCNTL_FLAGS)
/*
* Start with fault_pending_wqh and fault_wqh so they're more likely
* to be in the same cacheline.
*
* Locking order:
* fd_wqh.lock
* fault_pending_wqh.lock
* fault_wqh.lock
* event_wqh.lock
*
* To avoid deadlocks, IRQs must be disabled when taking any of the above locks,
* since fd_wqh.lock is taken by aio_poll() while it's holding a lock that's
* also taken in IRQ context.
*/
struct userfaultfd_ctx {
/* waitqueue head for the pending (i.e. not read) userfaults */
wait_queue_head_t fault_pending_wqh;
/* waitqueue head for the userfaults */
wait_queue_head_t fault_wqh;
/* waitqueue head for the pseudo fd to wakeup poll/read */
wait_queue_head_t fd_wqh;
/* waitqueue head for events */
wait_queue_head_t event_wqh;
/* a refile sequence protected by fault_pending_wqh lock */
seqcount_spinlock_t refile_seq;
/* pseudo fd refcounting */
refcount_t refcount;
/* userfaultfd syscall flags */
unsigned int flags;
/* features requested from the userspace */
unsigned int features;
/* released */
bool released;
/* memory mappings are changing because of non-cooperative event */
atomic_t mmap_changing;
/* mm with one ore more vmas attached to this userfaultfd_ctx */
struct mm_struct *mm;
};
extern vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason);
/* A combined operation mode + behavior flags. */