+ mm-oom_kill-have-the-oom-reaper-and-exit_mmap-traverse-the-maple-tree-in-opposite-orders.patch added to mm-new branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm/oom_kill: have the OOM reaper and exit_mmap() traverse the maple tree in opposite orders
has been added to the -mm mm-new branch.  Its filename is
     mm-oom_kill-have-the-oom-reaper-and-exit_mmap-traverse-the-maple-tree-in-opposite-orders.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-oom_kill-have-the-oom-reaper-and-exit_mmap-traverse-the-maple-tree-in-opposite-orders.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

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------------------------------------------------------
From: zhongjinji <zhongjinji@honor.com>
Subject: mm/oom_kill: have the OOM reaper and exit_mmap() traverse the maple tree in opposite orders
Date: Thu, 14 Aug 2025 21:55:55 +0800

When a process is OOM killed, if the OOM reaper and the thread running
exit_mmap() execute at the same time, both will traverse the vma's maple
tree along the same path.  They may easily unmap the same vma, causing
them to compete for the pte spinlock.  This increases unnecessary load,
causing the execution time of the OOM reaper and the thread running
exit_mmap() to increase.

When a process exits, exit_mmap() traverses the vma's maple tree from low
to high address.  To reduce the chance of unmapping the same vma
simultaneously, the OOM reaper should traverse vma's tree from high to low
address.  This reduces lock contention when unmapping the same vma.

Link: https://lkml.kernel.org/r/20250814135555.17493-4-zhongjinji@honor.com
Signed-off-by: zhongjinji <zhongjinji@honor.com>
Cc: Andre Almeida <andrealmeid@igalia.com>
Cc: Darren Hart <dvhart@infradead.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: David Rientjes <rientjes@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Joel Savitz <jsavitz@redhat.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Mariano Pache <npache@redhat.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Thomas Gleinxer <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/mm.h |    3 +++
 mm/oom_kill.c      |    9 +++++++--
 2 files changed, 10 insertions(+), 2 deletions(-)

--- a/include/linux/mm.h~mm-oom_kill-have-the-oom-reaper-and-exit_mmap-traverse-the-maple-tree-in-opposite-orders
+++ a/include/linux/mm.h
@@ -974,6 +974,9 @@ static inline void vma_iter_set(struct v
 #define for_each_vma_range(__vmi, __vma, __end)				\
 	while (((__vma) = vma_find(&(__vmi), (__end))) != NULL)
 
+#define for_each_vma_reverse(__vmi, __vma)					\
+	while (((__vma) = vma_prev(&(__vmi))) != NULL)
+
 #ifdef CONFIG_SHMEM
 /*
  * The vma_is_shmem is not inline because it is used only by slow
--- a/mm/oom_kill.c~mm-oom_kill-have-the-oom-reaper-and-exit_mmap-traverse-the-maple-tree-in-opposite-orders
+++ a/mm/oom_kill.c
@@ -517,7 +517,7 @@ static bool __oom_reap_task_mm(struct mm
 {
 	struct vm_area_struct *vma;
 	bool ret = true;
-	VMA_ITERATOR(vmi, mm, 0);
+	VMA_ITERATOR(vmi, mm, ULONG_MAX);
 
 	/*
 	 * Tell all users of get_user/copy_from_user etc... that the content
@@ -527,7 +527,12 @@ static bool __oom_reap_task_mm(struct mm
 	 */
 	mm_flags_set(MMF_UNSTABLE, mm);
 
-	for_each_vma(vmi, vma) {
+	/*
+	 * When two tasks unmap the same vma at the same time, they may contend for the
+	 * pte spinlock. To avoid traversing the same vma as exit_mmap unmap, traverse
+	 * the vma maple tree in reverse order.
+	 */
+	for_each_vma_reverse(vmi, vma) {
 		if (vma->vm_flags & (VM_HUGETLB|VM_PFNMAP))
 			continue;
 
_

Patches currently in -mm which might be from zhongjinji@honor.com are

futex-introduce-function-process_has_robust_futex.patch
mm-oom_kill-only-delay-oom-reaper-for-processes-using-robust-futexes.patch
mm-oom_kill-have-the-oom-reaper-and-exit_mmap-traverse-the-maple-tree-in-opposite-orders.patch