Do we want this on top?
----
>From 58b04ae6dc97b0105ea2651daca55cf2386f69b4 Mon Sep 17 00:00:00 2001
From: Michal Hocko <mhocko@xxxxxxxx>
Date: Thu, 9 Dec 2021 10:07:51 +0100
Subject: [PATCH] mm: drop MMF_OOM_SKIP from exit_mmap
MMF_OOM_SKIP used to play a synchronization role between exit_mmap and
oom repear in the past. Since the exclusive mmap_sem is held in
exit_mmap to cover all destructive operations the flag synchronization
is not needed anymore and we can safely drop it. Just make sure that
mm->mmap is set to NULL so that nobody will access the freed vma list.
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
---
mm/mmap.c | 23 +----------------------
1 file changed, 1 insertion(+), 22 deletions(-)
diff --git a/mm/mmap.c b/mm/mmap.c
index f4e09d390a07..0d6af9d89aa8 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -3129,28 +3129,6 @@ void exit_mmap(struct mm_struct *mm)
/* mm's last user has gone, and its about to be pulled down */
mmu_notifier_release(mm);
- if (unlikely(mm_is_oom_victim(mm))) {
- /*
- * Manually reap the mm to free as much memory as possible.
- * Then, as the oom reaper does, set MMF_OOM_SKIP to disregard
- * this mm from further consideration. Taking mm->mmap_lock for
- * write after setting MMF_OOM_SKIP will guarantee that the oom
- * reaper will not run on this mm again after mmap_lock is
- * dropped.
- *
- * Nothing can be holding mm->mmap_lock here and the above call
- * to mmu_notifier_release(mm) ensures mmu notifier callbacks in
- * __oom_reap_task_mm() will not block.
- *
- * This needs to be done before calling unlock_range(),
- * which clears VM_LOCKED, otherwise the oom reaper cannot
- * reliably test it.
- */
- (void)__oom_reap_task_mm(mm);
-
- set_bit(MMF_OOM_SKIP, &mm->flags);
- }
-
mmap_write_lock(mm);
if (mm->locked_vm)
unlock_range(mm->mmap, ULONG_MAX);
@@ -3180,6 +3158,7 @@ void exit_mmap(struct mm_struct *mm)
vma = remove_vma(vma);
cond_resched();
}
+ mm->mmap = NULL;
mmap_write_unlock(mm);
vm_unacct_memory(nr_accounted);
}
--
2.30.2
--
Michal Hocko
SUSE Labs
