Since commit 862e3073b3eed13f
("mm, oom: get rid of signal_struct::oom_victims")
changed to wait until MMF_OOM_SKIP is set rather than wait while
TIF_MEMDIE is set, rationale comment for commit e2fe14564d3316d1
("oom_reaper: close race with exiting task") needs to be updated.
While holding oom_lock can make sure that other threads waiting for
oom_lock at __alloc_pages_may_oom() are given a chance to call
get_page_from_freelist() after the OOM reaper called unmap_page_range()
via __oom_reap_task_mm(), it can defer calling of __oom_reap_task_mm().
Therefore, this patch moves oom_lock from __oom_reap_task_mm() to
oom_reap_task() (without any functional change). By doing so, the OOM
killer can call __oom_reap_task_mm() if we don't want to defer calling
of __oom_reap_task_mm() (e.g. when oom_evaluate_task() aborted by
finding existing OOM victim's mm without MMF_OOM_SKIP).
Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
---
mm/oom_kill.c | 39 +++++++++++++--------------------------
1 file changed, 13 insertions(+), 26 deletions(-)
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index ec9f11d..53b6e0c 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -467,28 +467,9 @@ static bool __oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm)
struct vm_area_struct *vma;
struct zap_details details = {.check_swap_entries = true,
.ignore_dirty = true};
- bool ret = true;
-
- /*
- * We have to make sure to not race with the victim exit path
- * and cause premature new oom victim selection:
- * __oom_reap_task_mm exit_mm
- * mmget_not_zero
- * mmput
- * atomic_dec_and_test
- * exit_oom_victim
- * [...]
- * out_of_memory
- * select_bad_process
- * # no TIF_MEMDIE task selects new victim
- * unmap_page_range # frees some memory
- */
- mutex_lock(&oom_lock);
- if (!down_read_trylock(&mm->mmap_sem)) {
- ret = false;
- goto unlock_oom;
- }
+ if (!down_read_trylock(&mm->mmap_sem))
+ return false;
/*
* increase mm_users only after we know we will reap something so
@@ -497,7 +478,7 @@ static bool __oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm)
*/
if (!mmget_not_zero(mm)) {
up_read(&mm->mmap_sem);
- goto unlock_oom;
+ return true;
}
/*
@@ -548,9 +529,7 @@ static bool __oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm)
* put the oom_reaper out of the way.
*/
mmput_async(mm);
-unlock_oom:
- mutex_unlock(&oom_lock);
- return ret;
+ return true;
}
#define MAX_OOM_REAP_RETRIES 10
@@ -560,8 +539,16 @@ static void oom_reap_task(struct task_struct *tsk)
struct mm_struct *mm = tsk->signal->oom_mm;
/* Retry the down_read_trylock(mmap_sem) a few times */
- while (attempts++ < MAX_OOM_REAP_RETRIES && !__oom_reap_task_mm(tsk, mm))
+ while (attempts++ < MAX_OOM_REAP_RETRIES) {
+ bool ret;
+
+ mutex_lock(&oom_lock);
+ ret = __oom_reap_task_mm(tsk, mm);
+ mutex_unlock(&oom_lock);
+ if (ret)
+ break;
schedule_timeout_idle(HZ/10);
+ }
if (attempts <= MAX_OOM_REAP_RETRIES)
goto done;
--
1.8.3.1
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