The patch titled
Subject: userfaultfd: move userfaultfd_ctx struct to header file
has been added to the -mm mm-unstable branch. Its filename is
userfaultfd-move-userfaultfd_ctx-struct-to-header-file.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/userfaultfd-move-userfaultfd_ctx-struct-to-header-file.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Lokesh Gidra <lokeshgidra@xxxxxxxxxx>
Subject: userfaultfd: move userfaultfd_ctx struct to header file
Date: Tue, 13 Feb 2024 13:57:39 -0800
Patch series "per-vma locks in userfaultfd", v6.
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 6):
Moving 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/20240213215741.3816570-1-lokeshgidra@xxxxxxxxxx
Link: https://lkml.kernel.org/r/20240213215741.3816570-2-lokeshgidra@xxxxxxxxxx
Signed-off-by: Lokesh Gidra <lokeshgidra@xxxxxxxxxx>
Reviewed-by: Mike Rapoport (IBM) <rppt@xxxxxxxxxx>
Reviewed-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Axel Rasmussen <axelrasmussen@xxxxxxxxxx>
Cc: Brian Geffon <bgeffon@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Jann Horn <jannh@xxxxxxxxxx>
Cc: Kalesh Singh <kaleshsingh@xxxxxxxxxx>
Cc: Lokesh Gidra <lokeshgidra@xxxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Nicolas Geoffray <ngeoffray@xxxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Cc: Tim Murray <timmurray@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/userfaultfd.c | 39 --------------------------------
include/linux/userfaultfd_k.h | 39 ++++++++++++++++++++++++++++++++
2 files changed, 39 insertions(+), 39 deletions(-)
--- a/fs/userfaultfd.c~userfaultfd-move-userfaultfd_ctx-struct-to-header-file
+++ a/fs/userfaultfd.c
@@ -50,45 +50,6 @@ static struct ctl_table vm_userfaultfd_t
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;
--- a/include/linux/userfaultfd_k.h~userfaultfd-move-userfaultfd_ctx-struct-to-header-file
+++ a/include/linux/userfaultfd_k.h
@@ -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. */
_
Patches currently in -mm which might be from lokeshgidra@xxxxxxxxxx are
userfaultfd-fix-return-error-if-mmap_changing-is-non-zero-in-move-ioctl.patch
userfaultfd-move-userfaultfd_ctx-struct-to-header-file.patch
userfaultfd-protect-mmap_changing-with-rw_sem-in-userfaulfd_ctx.patch
userfaultfd-use-per-vma-locks-in-userfaultfd-operations.patch
