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Subject[PATCH 2/3] mm: drop oom code from exit_mmap
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With the oom-killer being able to operate on locked pages, exit_mmap
does not need to ensure that oom_reap_task_mm is done before it can
proceed. Instead it can rely on mmap_lock write lock to prevent
oom-killer from operating on the vma tree while it's freeing page
tables. exit_mmap can hold mmap_lock read lock when unmapping vmas
and then take mmap_lock write lock before freeing page tables.

Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
include/linux/oom.h | 2 --
mm/mmap.c | 25 ++++++-------------------
mm/oom_kill.c | 2 +-
3 files changed, 7 insertions(+), 22 deletions(-)

diff --git a/include/linux/oom.h b/include/linux/oom.h
index 2db9a1432511..6cdf0772dbae 100644
--- a/include/linux/oom.h
+++ b/include/linux/oom.h
@@ -106,8 +106,6 @@ static inline vm_fault_t check_stable_address_space(struct mm_struct *mm)
return 0;
}

-bool __oom_reap_task_mm(struct mm_struct *mm);
-
long oom_badness(struct task_struct *p,
unsigned long totalpages);

diff --git a/mm/mmap.c b/mm/mmap.c
index 313b57d55a63..feaa840fb95d 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -3105,30 +3105,13 @@ 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.
- */
- (void)__oom_reap_task_mm(mm);
- set_bit(MMF_OOM_SKIP, &mm->flags);
- }
-
- mmap_write_lock(mm);
+ mmap_read_lock(mm);
arch_exit_mmap(mm);

vma = mm->mmap;
if (!vma) {
/* Can happen if dup_mmap() received an OOM */
- mmap_write_unlock(mm);
+ mmap_read_unlock(mm);
return;
}

@@ -3138,6 +3121,10 @@ void exit_mmap(struct mm_struct *mm)
/* update_hiwater_rss(mm) here? but nobody should be looking */
/* Use -1 here to ensure all VMAs in the mm are unmapped */
unmap_vmas(&tlb, vma, 0, -1);
+ mmap_read_unlock(mm);
+ /* Set MMF_OOM_SKIP to disregard this mm from further consideration.*/
+ set_bit(MMF_OOM_SKIP, &mm->flags);
+ mmap_write_lock(mm);
free_pgtables(&tlb, vma, FIRST_USER_ADDRESS, USER_PGTABLES_CEILING);
tlb_finish_mmu(&tlb);

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 49d7df39b02d..36355b162727 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -509,7 +509,7 @@ static DECLARE_WAIT_QUEUE_HEAD(oom_reaper_wait);
static struct task_struct *oom_reaper_list;
static DEFINE_SPINLOCK(oom_reaper_lock);

-bool __oom_reap_task_mm(struct mm_struct *mm)
+static bool __oom_reap_task_mm(struct mm_struct *mm)
{
struct vm_area_struct *vma;
bool ret = true;
--
2.36.0.512.ge40c2bad7a-goog
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