linux-kernel - Re: [PATCH v2] mm: terminate shrink

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Date:   Sat, 9 Dec 2017 21:44:20 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     David Rientjes <rientjes@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>
Cc:     akpm@...ux-foundation.org, mhocko@...e.com, hannes@...xchg.org,
        hillf.zj@...baba-inc.com, minchan@...nel.org,
        mgorman@...hsingularity.net, ying.huang@...el.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        timmurray@...gle.com, tkjos@...gle.com
Subject: Re: [PATCH v2] mm: terminate shrink_slab loop if signal is pending

On 2017/12/09 6:02, David Rientjes wrote:
> On Thu, 7 Dec 2017, Suren Baghdasaryan wrote:
> 
>> Slab shrinkers can be quite time consuming and when signal
>> is pending they can delay handling of the signal. If fatal
>> signal is pending there is no point in shrinking that process
>> since it will be killed anyway. This change checks for pending
>> fatal signals inside shrink_slab loop and if one is detected
>> terminates this loop early.
>>
> 
> I've proposed a similar patch in the past, but for a check on TIF_MEMDIE, 
> which would today be a tsk_is_oom_victim(current), since we had observed 
> lengthy stalls in reclaim that would have been prevented if the oom victim 
> had exited out, returned back to the page allocator, allocated with 
> ALLOC_NO_WATERMARKS, and proceeded to quickly exit.
> 
> I'm not sure that all fatal_signal_pending() tasks should get the same 
> treatment, but I understand the point that the task is killed and should 
> free memory when it fully exits.  How much memory is unknown.
> 
We can use __GFP_KILLABLE. Unless there is performance impact for checking
fatal_siganl_pending(), allowing only fatal_signal_pending() threads with
__GFP_KILLABLE to bail out (without using memory reserves) should be safe.