From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f198.google.com (mail-pf0-f198.google.com [209.85.192.198]) by kanga.kvack.org (Postfix) with ESMTP id 5B5F76B038A for ; Mon, 13 Mar 2017 11:17:58 -0400 (EDT) Received: by mail-pf0-f198.google.com with SMTP id w189so299209108pfb.4 for ; Mon, 13 Mar 2017 08:17:58 -0700 (PDT) Received: from mail-pf0-x235.google.com (mail-pf0-x235.google.com. [2607:f8b0:400e:c00::235]) by mx.google.com with ESMTPS id j10si11712199pfa.40.2017.03.13.08.17.57 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 13 Mar 2017 08:17:57 -0700 (PDT) Received: by mail-pf0-x235.google.com with SMTP id j5so70480167pfb.2 for ; Mon, 13 Mar 2017 08:17:57 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20170313083314.GA31518@dhcp22.suse.cz> References: <1489316770-25362-1-git-send-email-ysxie@foxmail.com> <20170313083314.GA31518@dhcp22.suse.cz> From: Shakeel Butt Date: Mon, 13 Mar 2017 08:17:56 -0700 Message-ID: Subject: Re: [PATCH v3 RFC] mm/vmscan: more restrictive condition for retry of shrink_zones Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Yisheng Xie , Andrew Morton , Johannes Weiner , Mel Gorman , Vlastimil Babka , riel@redhat.com, Linux MM , LKML , xieyisheng1@huawei.com, guohanjun@huawei.com, Xishi Qiu On Mon, Mar 13, 2017 at 1:33 AM, Michal Hocko wrote: > Please do not post new version after a single feedback and try to wait > for more review to accumulate. This is in the 3rd version and it is not > clear why it is still an RFC. > > On Sun 12-03-17 19:06:10, Yisheng Xie wrote: >> From: Yisheng Xie >> >> When we enter do_try_to_free_pages, the may_thrash is always clear, and >> it will retry shrink zones to tap cgroup's reserves memory by setting >> may_thrash when the former shrink_zones reclaim nothing. >> >> However, when memcg is disabled or on legacy hierarchy, it should not do >> this useless retry at all, for we do not have any cgroup's reserves >> memory to tap, and we have already done hard work but made no progress. >> >> To avoid this time costly and useless retrying, add a stub function >> mem_cgroup_thrashed() and return true when memcg is disabled or on >> legacy hierarchy. > > Have you actually seen this as a bad behavior? On which workload? Or > have spotted this by the code review? > > Please note that more than _what_ it is more interesting _why_ the patch > has been prepared. > > I agree the current additional round of reclaim is just lame because we > are trying hard to control the retry logic from the page allocator which > is a sufficient justification to fix this IMO. But I really hate the > name. At this point we do not have any idea that the memcg is trashing > as the name of the function suggests. > > All of them simply might not have any reclaimable pages. So I would > suggest either a better name e.g. memcg_allow_lowmem_reclaim() or, > preferably, fix this properly. E.g. something like the following. > --- > diff --git a/mm/vmscan.c b/mm/vmscan.c > index bae698484e8e..989ba9761921 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -99,6 +99,9 @@ struct scan_control { > /* Can cgroups be reclaimed below their normal consumption range? */ > unsigned int may_thrash:1; > > + /* Did we have any memcg protected by the low limit */ > + unsigned int memcg_low_protection:1; > + > unsigned int hibernation_mode:1; > > /* One of the zones is ready for compaction */ > @@ -2513,6 +2516,7 @@ static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc) > if (mem_cgroup_low(root, memcg)) { > if (!sc->may_thrash) > continue; > + sc->memcg_low_protection = true; I think you wanted to put this statement before the continue otherwise it will just disable the sc->may_thrash (second reclaim pass) altogether. > mem_cgroup_events(memcg, MEMCG_LOW, 1); > } > > @@ -2774,7 +2778,7 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist, > return 1; > > /* Untapped cgroup reserves? Don't OOM, retry. */ > - if (!sc->may_thrash) { > + if ( sc->memcg_low_protection && !sc->may_thrash) { > sc->priority = initial_priority; > sc->may_thrash = 1; > goto retry; > -- > Michal Hocko > SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org