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

[David Rientjes <rientjes@google.com>]

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,