On Mon 12-12-16 19:55:52, Tetsuo Handa wrote:
> 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.
True.
> 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).
But I fail to understand this part of the changelog. It sounds like a
preparatory for other changes. There doesn't seem to be any other user
of __oom_reap_task_mm in the current tree.
Please send a patch which removes the comment which is no longer true
on its own and feel free to add
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
but do not make other changes if you do not have any follow up patch
which would benefit from that.
Thanks!
> 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
>
--
Michal Hocko
SUSE Labs
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