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[140.211.169.12]) by mx.google.com with ESMTPS id h88si2219937pfa.49.2019.01.28.11.54.26 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 28 Jan 2019 11:54:26 -0800 (PST) Received-SPF: pass (google.com: domain of akpm@linux-foundation.org designates 140.211.169.12 as permitted sender) client-ip=140.211.169.12; Authentication-Results: mx.google.com; spf=pass (google.com: domain of akpm@linux-foundation.org designates 140.211.169.12 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org Received: from akpm3.svl.corp.google.com (unknown [104.133.8.65]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id 103181AE5; Mon, 28 Jan 2019 19:54:25 +0000 (UTC) Date: Mon, 28 Jan 2019 11:54:24 -0800 From: Andrew Morton To: Rik van Riel Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, kernel-team@fb.com, Johannes Weiner , Chris Mason , Roman Gushchin , Michal Hocko Subject: Re: [PATCH] mm,slab,vmscan: accumulate gradual pressure on small slabs Message-Id: <20190128115424.df3f4647023e9e43e75afe67@linux-foundation.org> In-Reply-To: <20190128143535.7767c397@imladris.surriel.com> References: <20190128143535.7767c397@imladris.surriel.com> X-Mailer: Sylpheed 3.6.0 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit 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 Mon, 28 Jan 2019 14:35:35 -0500 Rik van Riel wrote: > There are a few issues with the way the number of slab objects to > scan is calculated in do_shrink_slab. First, for zero-seek slabs, > we could leave the last object around forever. That could result > in pinning a dying cgroup into memory, instead of reclaiming it. > The fix for that is trivial. > > Secondly, small slabs receive much more pressure, relative to their > size, than larger slabs, due to "rounding up" the minimum number of > scanned objects to batch_size. > > We can keep the pressure on all slabs equal relative to their size > by accumulating the scan pressure on small slabs over time, resulting > in sometimes scanning an object, instead of always scanning several. > > This results in lower system CPU use, and a lower major fault rate, > as actively used entries from smaller caches get reclaimed less > aggressively, and need to be reloaded/recreated less often. > > Fixes: 4b85afbdacd2 ("mm: zero-seek shrinkers") > Fixes: 172b06c32b94 ("mm: slowly shrink slabs with a relatively small number of objects") > Cc: Johannes Weiner > Cc: Chris Mason > Cc: Roman Gushchin > Cc: kernel-team@fb.com > Tested-by: Chris Mason I added your Signed-off-by: > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -488,18 +488,28 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl, > * them aggressively under memory pressure to keep > * them from causing refetches in the IO caches. > */ > - delta = freeable / 2; > + delta = (freeable + 1)/ 2; > } > > /* > * Make sure we apply some minimal pressure on default priority > - * even on small cgroups. Stale objects are not only consuming memory > + * even on small cgroups, by accumulating pressure across multiple > + * slab shrinker runs. Stale objects are not only consuming memory > * by themselves, but can also hold a reference to a dying cgroup, > * preventing it from being reclaimed. A dying cgroup with all > * corresponding structures like per-cpu stats and kmem caches > * can be really big, so it may lead to a significant waste of memory. > */ > - delta = max_t(unsigned long long, delta, min(freeable, batch_size)); > + if (!delta) { > + shrinker->small_scan += freeable; > + > + delta = shrinker->small_scan >> priority; > + shrinker->small_scan -= delta << priority; > + > + delta *= 4; > + do_div(delta, shrinker->seeks); What prevents shrinker->small_scan from over- or underflowing over time? > + } > > total_scan += delta; > if (total_scan < 0) { I'll add this: whitespace fixes, per Roman --- a/mm/vmscan.c~mmslabvmscan-accumulate-gradual-pressure-on-small-slabs-fix +++ a/mm/vmscan.c @@ -488,7 +488,7 @@ static unsigned long do_shrink_slab(stru * them aggressively under memory pressure to keep * them from causing refetches in the IO caches. */ - delta = (freeable + 1)/ 2; + delta = (freeable + 1) / 2; } /* @@ -508,7 +508,6 @@ static unsigned long do_shrink_slab(stru delta *= 4; do_div(delta, shrinker->seeks); - } total_scan += delta; _