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[195.135.220.15]) by mx.google.com with ESMTPS id g15si27026660ejm.175.2019.08.06.03.28.47 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 06 Aug 2019 03:28:47 -0700 (PDT) Received-SPF: softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) client-ip=195.135.220.15; Authentication-Results: mx.google.com; spf=softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) smtp.mailfrom=mhocko@kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=kernel.org X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id EEB04AF38; Tue, 6 Aug 2019 10:28:46 +0000 (UTC) Date: Tue, 6 Aug 2019 12:28:45 +0200 From: Michal Hocko To: Yafang Shao Cc: Mel Gorman , Andrew Morton , Linux MM , Daniel Jordan , Christoph Lameter , Yafang Shao Subject: Re: [PATCH v2] mm/vmscan: shrink slab in node reclaim Message-ID: <20190806102845.GP11812@dhcp22.suse.cz> References: <1565075940-23121-1-git-send-email-laoar.shao@gmail.com> <20190806073525.GC11812@dhcp22.suse.cz> <20190806074137.GE11812@dhcp22.suse.cz> <20190806090516.GM11812@dhcp22.suse.cz> <20190806092531.GN11812@dhcp22.suse.cz> <20190806095028.GG2739@techsingularity.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue 06-08-19 17:54:02, Yafang Shao wrote: > On Tue, Aug 6, 2019 at 5:50 PM Mel Gorman wrote: > > > > On Tue, Aug 06, 2019 at 11:25:31AM +0200, Michal Hocko wrote: > > > On Tue 06-08-19 17:15:05, Yafang Shao wrote: > > > > On Tue, Aug 6, 2019 at 5:05 PM Michal Hocko wrote: > > > [...] > > > > > > As you said, the direct reclaim path set it to 1, but the > > > > > > __node_reclaim() forgot to process may_shrink_slab. > > > > > > > > > > OK, I am blind obviously. Sorry about that. Anyway, why cannot we simply > > > > > get back to the original behavior by setting may_shrink_slab in that > > > > > path as well? > > > > > > > > You mean do it as the commit 0ff38490c836 did before ? > > > > I haven't check in which commit the shrink_slab() is removed from > > > > > > What I've had in mind was essentially this: > > > > > > diff --git a/mm/vmscan.c b/mm/vmscan.c > > > index 7889f583ced9..8011288a80e2 100644 > > > --- a/mm/vmscan.c > > > +++ b/mm/vmscan.c > > > @@ -4088,6 +4093,7 @@ static int __node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned in > > > .may_unmap = !!(node_reclaim_mode & RECLAIM_UNMAP), > > > .may_swap = 1, > > > .reclaim_idx = gfp_zone(gfp_mask), > > > + .may_shrinkslab = 1; > > > }; > > > > > > trace_mm_vmscan_node_reclaim_begin(pgdat->node_id, order, > > > > > > shrink_node path already does shrink slab when the flag allows that. In > > > other words get us back to before 1c30844d2dfe because that has clearly > > > changed the long term node reclaim behavior just recently. > > > > I'd be fine with this change. It was not intentional to significantly > > change the behaviour of node reclaim in that patch. > > > > But if we do it like this, there will be bug in the knob vm.min_slab_ratio. > Right ? Yes, and the answer for that is a question why do we even care? Which real life workload does suffer from the of min_slab_ratio misbehavior. Also it is much more preferred to fix an obvious bug/omission which lack of may_shrinkslab in node reclaim seem to be than a larger rewrite with a harder to see changes. Really, I wouldn't be opposing normally but node_reclaim is an odd ball rarely used and changing its behavior based on some trivial testing doesn't sound very convincing to me. -- Michal Hocko SUSE Labs