Re: [PATCH] mm, oom: distinguish blockable mode for mmu notifiers

David Rientjes
2018-07-24T21:07:49Z

On Tue, 24 Jul 2018, Michal Hocko wrote:

> oom_reap_task_mm should return false when __oom_reap_task_mm return
> false. This is what my patch did but it seems this changed by
> http://www.ozlabs.org/~akpm/mmotm/broken-out/mm-oom-remove-oom_lock-from-oom_reaper.patch
> so that one should be fixed.
>
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 104ef4a01a55..88657e018714 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -565,7 +565,7 @@ static bool oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm)
> /* failed to reap part of the address space. Try again later */
> if (!__oom_reap_task_mm(mm)) {
> up_read(&mm->mmap_sem);
> - return true;
> + return false;
> }
>
> pr_info("oom_reaper: reaped process %d (%s), now anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB\n",
>
>
> On top of that the proposed cleanup looks as follows:
>
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 88657e018714..4e185a282b3d 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -541,8 +541,16 @@ bool __oom_reap_task_mm(struct mm_struct *mm)
> return ret;
> }
>
> +/*
> + * Reaps the address space of the give task.
> + *
> + * Returns true on success and false if none or part of the address space
> + * has been reclaimed and the caller should retry later.
> + */
> static bool oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm)
> {
> + bool ret = true;
> +
> if (!down_read_trylock(&mm->mmap_sem)) {
> trace_skip_task_reaping(tsk->pid);
> return false;
> @@ -555,28 +563,28 @@ static bool oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm)
> * down_write();up_write() cycle in exit_mmap().
> */
> if (test_bit(MMF_OOM_SKIP, &mm->flags)) {
> - up_read(&mm->mmap_sem);
> trace_skip_task_reaping(tsk->pid);
> - return true;
> + goto out_unlock;
> }
>
> trace_start_task_reaping(tsk->pid);
>
> /* failed to reap part of the address space. Try again later */
> - if (!__oom_reap_task_mm(mm)) {
> - up_read(&mm->mmap_sem);
> - return false;
> - }
> + ret = __oom_reap_task_mm(mm);
> + if (!ret)
> + goto out_finish;
>
> pr_info("oom_reaper: reaped process %d (%s), now anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB\n",
> task_pid_nr(tsk), tsk->comm,
> K(get_mm_counter(mm, MM_ANONPAGES)),
> K(get_mm_counter(mm, MM_FILEPAGES)),
> K(get_mm_counter(mm, MM_SHMEMPAGES)));
> +out_finish:
> + trace_finish_task_reaping(tsk->pid);
> +out_unlock:
> up_read(&mm->mmap_sem);
>
> - trace_finish_task_reaping(tsk->pid);
> - return true;
> + return ret;
> }
>
> #define MAX_OOM_REAP_RETRIES 10

I think we still want to trace when reaping was skipped to know that the
oom reaper will retry again later.

mm/oom_kill.c: clean up oom_reap_task_mm() fix

indicate reaping has been partially skipped so we can expect future skips
or another start before finish.

Signed-off-by: David Rientjes <rientjes@google.com>
---
mm/oom_kill.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -569,10 +569,12 @@ static bool oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm)

trace_start_task_reaping(tsk->pid);

- /* failed to reap part of the address space. Try again later */
ret = __oom_reap_task_mm(mm);
- if (!ret)
+ if (!ret) {
+ /* Failed to reap part of the address space. Try again later */
+ trace_skip_task_reaping(tsk->pid);
goto out_finish;
+ }

pr_info("oom_reaper: reaped process %d (%s), now anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB\n",
task_pid_nr(tsk), tsk->comm,
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