Re: [PATCH 8/9] mm: page_alloc: wait for OOM killer progress before retrying

[Michal Hocko <mhocko@suse.cz>]

On Mon 27-04-15 15:05:54, Johannes Weiner wrote:
> There is not much point in rushing back to the freelists and burning
> CPU cycles in direct reclaim when somebody else is in the process of
> OOM killing, or right after issuing a kill ourselves, because it could
> take some time for the OOM victim to release memory.
> 
> This is a very cold error path, so there is not much hurry.  Use the
> OOM victim waitqueue to wait for victims to actually exit, which is a
> solid signal that the memory pinned by those tasks has been released.
> 
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>

Looks good to me. One minor thing/suggestion below.
Acked-by: Michal Hocko <mhocko@suse.cz>

> ---
>  mm/oom_kill.c   | 11 +++++++----
>  mm/page_alloc.c | 43 ++++++++++++++++++++++++++-----------------
>  2 files changed, 33 insertions(+), 21 deletions(-)
> 
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 5cfda39..823f87e 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -711,12 +711,15 @@ bool out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
>  		killed = 1;
>  	}
>  out:
> +	if (test_thread_flag(TIF_MEMDIE))
> +		return true;
>  	/*
> -	 * Give the killed threads a good chance of exiting before trying to
> -	 * allocate memory again.
> +	 * Wait for any outstanding OOM victims to die.  In rare cases
> +	 * victims can get stuck behind the allocating tasks, so the
> +	 * wait needs to be bounded.  It's crude alright, but cheaper
> +	 * than keeping a global dependency tree between all tasks.
>  	 */
> -	if (killed)
> -		schedule_timeout_killable(1);
> +	wait_event_timeout(oom_victims_wait, !atomic_read(&oom_victims), 5*HZ);

WARN(!wait_event_timeout(...), "OOM victim has hard time to finish. OOM deadlock?")

or something along those lines? It would tell the admin that something
fishy is going here.

>  
>  	return true;
>  }
[...]
-- 
Michal Hocko
SUSE Labs

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