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[209.85.220.65]) by mx.google.com with SMTPS id n137sor5258546yba.166.2019.02.20.08.20.23 for (Google Transport Security); Wed, 20 Feb 2019 08:20:23 -0800 (PST) Received-SPF: pass (google.com: domain of hannes@cmpxchg.org designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; Authentication-Results: mx.google.com; dkim=pass header.i=@cmpxchg-org.20150623.gappssmtp.com header.s=20150623 header.b="Kw/tJPZQ"; spf=pass (google.com: domain of hannes@cmpxchg.org designates 209.85.220.65 as permitted sender) smtp.mailfrom=hannes@cmpxchg.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=cmpxchg.org DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cmpxchg-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=C070tjgZJxeeM7qSOkI80GMDNtIZkLi+xqFiicAZtLg=; b=Kw/tJPZQVwsHlVFpahkttIFQss0Eipp5XPVuDSea8auNp+jXZgZaQInhaP5RWYuzjf gvUf9FmsQQ/fuztL1dblZUSAIUR9TgRJBm7m3zr51zMcEYfKKrZ10Hw9uP7YX43YmdLX C/AyIPk5gH9TKLYM0mpLa/RLhcU0aepE36Yg5IYCUy9wNLFJTt+XT/EOK6v1O29O5e8V G1kX9JR4zHR+7EMAHgfpnhYMsl/BIwPJjJtVp3gxZPiXiN5PSSof6zUKdXlU5ADVVxxc MEuwxE16uexTQU3v82WA6ZmU9pGBHLooUNGoDqBWwRzYFHYRN7IJjuPgtIXo4fubEPVD rJBQ== X-Google-Smtp-Source: AHgI3IZN1W/wbKuBXgVLSt798kyCnFIfqASvAzckD4HrIGMC9bsKeYF5LF5F7AKF7bKQac8nfIa2MA== X-Received: by 2002:a25:c887:: with SMTP id y129mr29225474ybf.398.1550679622984; Wed, 20 Feb 2019 08:20:22 -0800 (PST) Received: from localhost ([2620:10d:c091:200::7:9eba]) by smtp.gmail.com with ESMTPSA id x82sm39758ywd.11.2019.02.20.08.20.21 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Wed, 20 Feb 2019 08:20:22 -0800 (PST) Date: Wed, 20 Feb 2019 11:20:21 -0500 From: Johannes Weiner To: Dave Chinner Cc: Roman Gushchin , "lsf-pc@lists.linux-foundation.org" , "linux-fsdevel@vger.kernel.org" , "linux-mm@kvack.org" , "riel@surriel.com" , "dchinner@redhat.com" , "guroan@gmail.com" , Kernel Team Subject: Re: [LSF/MM TOPIC] dying memory cgroups and slab reclaim issues Message-ID: <20190220162021.GB12866@cmpxchg.org> References: <20190219071329.GA7827@castle.DHCP.thefacebook.com> <20190220024723.GA20682@dastard> <20190220055031.GA23020@dastard> <20190220072707.GB23020@dastard> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190220072707.GB23020@dastard> User-Agent: Mutt/1.11.2 (2019-01-07) 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 Wed, Feb 20, 2019 at 06:27:07PM +1100, Dave Chinner wrote: > freeable = 1 > > ratio 4.15 priority 4.16 4.18 new > 1:100 1 12 0 batch 1 > 1.32 1 9 0 batch 1 > 1:12 1 6 0 batch 1 > 1:6 1 3 0 batch 1 > 1:1 1 1 1 batch 1 > @@ -479,7 +479,16 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl, > > total_scan = nr; > if (shrinker->seeks) { > - delta = freeable >> priority; > + /* > + * Use a small non-zero offset for delta so that if the scan > + * priority is low we always accumulate some pressure on caches > + * that have few freeable objects in them. This allows light > + * memory pressure to turn over caches with few freeable objects > + * slowly without the need for memory pressure priority to wind > + * up to the point where (freeable >> priority) is non-zero. > + */ > + delta = ilog2(freeable); The idea makes sense to me, but log2 fails us when freeable is 1. fls() should work, though. > + delta += freeable >> priority; > delta *= 4; > do_div(delta, shrinker->seeks); > } else {