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mm,oom_reaper: reduce find_lock_task_mm() usage 

Patch series "fortify oom killer even more", v2.

This patch (of 9):

__oom_reap_task() can be simplified a bit if it receives a valid mm from
oom_reap_task() which also uses that mm when __oom_reap_task() failed.
We can drop one find_lock_task_mm() call and also make the
__oom_reap_task() code flow easier to follow.  Moreover, this will make
later patch in the series easier to review.  Pinning mm's mm_count for
longer time is not really harmful because this will not pin much memory.

This patch doesn't introduce any functional change.

Link: http://lkml.kernel.org/r/1472119394-11342-2-git-send-email-mhocko@kernel.org
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Michal Hocko <mhocko@suse.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Vladimir Davydov <vdavydov@parallels.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Tetsuo Handa 2016-10-07 16:58:45 -07:00 committed by Linus Torvalds
parent 6b53491598
commit 7ebffa4555
1 changed files with 38 additions and 43 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

59
mm/oom_kill.c
View File

@ -463,12 +463,10 @@ static DECLARE_WAIT_QUEUE_HEAD(oom_reaper_wait);
static struct task_struct *oom_reaper_list;
static DEFINE_SPINLOCK(oom_reaper_lock);
static bool __oom_reap_task(struct task_struct *tsk)
static bool __oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm)
{
struct mmu_gather tlb;
struct vm_area_struct *vma;
struct mm_struct *mm = NULL;
struct task_struct *p;
struct zap_details details = {.check_swap_entries = true,
.ignore_dirty = true};
bool ret = true;
@ -476,7 +474,7 @@ static bool __oom_reap_task(struct task_struct *tsk)
/*
* We have to make sure to not race with the victim exit path
* and cause premature new oom victim selection:
* __oom_reap_task exit_mm
* __oom_reap_task_mm exit_mm
* mmget_not_zero
* mmput
* atomic_dec_and_test
@ -489,22 +487,9 @@ static bool __oom_reap_task(struct task_struct *tsk)
*/
mutex_lock(&oom_lock);
/*
* Make sure we find the associated mm_struct even when the particular
* thread has already terminated and cleared its mm.
* We might have race with exit path so consider our work done if there
* is no mm.
*/
p = find_lock_task_mm(tsk);
if (!p)
goto unlock_oom;
mm = p->mm;
atomic_inc(&mm->mm_count);
task_unlock(p);
if (!down_read_trylock(&mm->mmap_sem)) {
ret = false;
goto mm_drop;
goto unlock_oom;
}
/*
@ -514,7 +499,7 @@ static bool __oom_reap_task(struct task_struct *tsk)
*/
if (!mmget_not_zero(mm)) {
up_read(&mm->mmap_sem);
goto mm_drop;
goto unlock_oom;
}
tlb_gather_mmu(&tlb, mm, 0, -1);
@ -562,8 +547,6 @@ static bool __oom_reap_task(struct task_struct *tsk)
* put the oom_reaper out of the way.
*/
mmput_async(mm);
mm_drop:
mmdrop(mm);
unlock_oom:
mutex_unlock(&oom_lock);
return ret;
@ -573,13 +556,27 @@ unlock_oom:
static void oom_reap_task(struct task_struct *tsk)
{
int attempts = 0;
struct mm_struct *mm = NULL;
struct task_struct *p = find_lock_task_mm(tsk);
/*
* Make sure we find the associated mm_struct even when the particular
* thread has already terminated and cleared its mm.
* We might have race with exit path so consider our work done if there
* is no mm.
*/
if (!p)
goto done;
mm = p->mm;
atomic_inc(&mm->mm_count);
task_unlock(p);
/* Retry the down_read_trylock(mmap_sem) a few times */
while (attempts++ < MAX_OOM_REAP_RETRIES && !__oom_reap_task(tsk))
while (attempts++ < MAX_OOM_REAP_RETRIES && !__oom_reap_task_mm(tsk, mm))
schedule_timeout_idle(HZ/10);
if (attempts > MAX_OOM_REAP_RETRIES) {
struct task_struct *p;
if (attempts <= MAX_OOM_REAP_RETRIES)
goto done;
pr_info("oom_reaper: unable to reap pid:%d (%s)\n",
task_pid_nr(tsk), tsk->comm);
@ -590,19 +587,14 @@ static void oom_reap_task(struct task_struct *tsk)
* so hide the mm from the oom killer so that it can move on
* to another task with a different mm struct.
*/
p = find_lock_task_mm(tsk);
if (p) {
if (test_and_set_bit(MMF_OOM_NOT_REAPABLE, &p->mm->flags)) {
if (test_and_set_bit(MMF_OOM_NOT_REAPABLE, &mm->flags)) {
pr_info("oom_reaper: giving up pid:%d (%s)\n",
task_pid_nr(tsk), tsk->comm);
set_bit(MMF_OOM_REAPED, &p->mm->flags);
set_bit(MMF_OOM_REAPED, &mm->flags);
}
task_unlock(p);
}
debug_show_all_locks();
}
done:
/*
* Clear TIF_MEMDIE because the task shouldn't be sitting on a
* reasonably reclaimable memory anymore or it is not a good candidate
@ -614,6 +606,9 @@ static void oom_reap_task(struct task_struct *tsk)
/* Drop a reference taken by wake_oom_reaper */
put_task_struct(tsk);
/* Drop a reference taken above. */
if (mm)
mmdrop(mm);
}
static int oom_reaper(void *unused)