From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753809AbdLIDQe (ORCPT ); Fri, 8 Dec 2017 22:16:34 -0500 Received: from mail-wr0-f194.google.com ([209.85.128.194]:42192 "EHLO mail-wr0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753453AbdLIDQa (ORCPT ); Fri, 8 Dec 2017 22:16:30 -0500 X-Google-Smtp-Source: AGs4zMYv6mEOQkM40OqfDTFxPFhNICP3Yaa8/jszLbti/HkbRF8nEazEdyrkToIAJBBknBg1O8IS9KUwf/8qX0UDijs= MIME-Version: 1.0 In-Reply-To: References: <20171208012305.83134-1-surenb@google.com> From: Suren Baghdasaryan Date: Fri, 8 Dec 2017 19:16:28 -0800 Message-ID: Subject: Re: [PATCH v2] mm: terminate shrink_slab loop if signal is pending To: David Rientjes Cc: Andrew Morton , mhocko@suse.com, Johannes Weiner , hillf.zj@alibaba-inc.com, minchan@kernel.org, mgorman@techsingularity.net, ying.huang@intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Tim Murray , Todd Kjos Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Dec 8, 2017 at 1:02 PM, 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. > Thanks for the input. For my particular use case TIF_MEMDIE check would not help because I'm trying to kill a process before OOM kicks in, however the approach is interesting and provides food for thought. > > Signed-off-by: Suren Baghdasaryan >> >> --- >> V2: >> Sergey Senozhatsky: >> - Fix missing parentheses >> --- >> mm/vmscan.c | 7 +++++++ >> 1 file changed, 7 insertions(+) >> >> diff --git a/mm/vmscan.c b/mm/vmscan.c >> index c02c850ea349..28e4bdc72c16 100644 >> --- a/mm/vmscan.c >> +++ b/mm/vmscan.c >> @@ -486,6 +486,13 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid, >> .memcg = memcg, >> }; >> >> + /* >> + * We are about to die and free our memory. >> + * Stop shrinking which might delay signal handling. >> + */ >> + if (unlikely(fatal_signal_pending(current))) >> + break; >> + >> /* >> * If kernel memory accounting is disabled, we ignore >> * SHRINKER_MEMCG_AWARE flag and call all shrinkers