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[209.85.220.65]) by mx.google.com with SMTPS id w7sor1970486qtk.20.2019.08.07.11.34.37 for (Google Transport Security); Wed, 07 Aug 2019 11:34:37 -0700 (PDT) Received-SPF: pass (google.com: domain of htejun@gmail.com designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=R644OPU+; spf=pass (google.com: domain of htejun@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=htejun@gmail.com; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=kernel.org DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=TEd6gatoycG7ZYK/wRTlCi/eISRx26y7juuHAC9jUEs=; b=R644OPU+lCko3k9nDXGu9/A/vuDcJn94rJoMUPsDRCffxsG+isnp+BHBLQmc2K644e 66mQuGkZTGxAke75vOwmSvJK6B7tThNNgU17Mmy0pGVSIX7MQcF/72c5IwF+SVKe2+/9 3vXSRys0roMn1jdcB9qW6Ab8phv2F8C6FUUrmfEUu1zHhqC8meLDYyMaehtDUQwJF5bQ Y8GRTNQsLFdruJQs1xnvhyznDmk+7799OjLS/bJHXjEXyrGCjSTajeSkhizcSbuqKREl DPUrIKRtYKK8ndWxQKW2D8e2SYP9w65swXBr4FQtUapMvV0tAHkSYCN+X0SubrlfmUMZ lRmQ== X-Google-Smtp-Source: APXvYqw/m3khFk3Yualfy2xpN4sanvEEAmz6JBxD6EOIZ0rs6tDT7YTG6mbRbwiCk+s0QUksrpFdBw== X-Received: by 2002:ac8:2439:: with SMTP id c54mr9364734qtc.160.1565202876678; Wed, 07 Aug 2019 11:34:36 -0700 (PDT) Received: from localhost ([2620:10d:c091:500::6ac7]) by smtp.gmail.com with ESMTPSA id i27sm37896195qkk.58.2019.08.07.11.34.35 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 07 Aug 2019 11:34:36 -0700 (PDT) Date: Wed, 7 Aug 2019 11:34:34 -0700 From: Tejun Heo To: Andrew Morton Cc: axboe@kernel.dk, jack@suse.cz, hannes@cmpxchg.org, mhocko@kernel.org, vdavydov.dev@gmail.com, cgroups@vger.kernel.org, linux-mm@kvack.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com, guro@fb.com Subject: Re: [PATCH 4/4] writeback, memcg: Implement foreign dirty flushing Message-ID: <20190807183434.GN136335@devbig004.ftw2.facebook.com> References: <20190803140155.181190-1-tj@kernel.org> <20190803140155.181190-5-tj@kernel.org> <20190806160306.5330bd4fdddf357db4b7086c@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190806160306.5330bd4fdddf357db4b7086c@linux-foundation.org> User-Agent: Mutt/1.5.21 (2010-09-15) 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: Hello, On Tue, Aug 06, 2019 at 04:03:06PM -0700, Andrew Morton wrote: > > + if (i < MEMCG_CGWB_FRN_CNT) { > > + unsigned long update_intv = > > + min_t(unsigned long, HZ, > > + msecs_to_jiffies(dirty_expire_interval * 10) / 8); > > An explanation of what's going on here would be helpful. > > Why "* 1.25" and not, umm "* 1.24"? Just because /8 is cheaper. It's likely that a fairly wide range of numbers are okay for the above. I'll add some comment to explain that and why the specific constants are picked. > > +void mem_cgroup_flush_foreign(struct bdi_writeback *wb) > > +{ > > + struct mem_cgroup *memcg = mem_cgroup_from_css(wb->memcg_css); > > + unsigned long intv = msecs_to_jiffies(dirty_expire_interval * 10); > > Ditto. This is just dirty expiration. If the dirty data has expired, writeback must already be in progress by its bdi_wb, so there's no reason to scheduler foreign writeback. Will add a comment. Thanks. -- tejun