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[209.85.220.65]) by mx.google.com with SMTPS id j2sor6355923ywf.51.2019.04.12.13.07.28 for (Google Transport Security); Fri, 12 Apr 2019 13:07:28 -0700 (PDT) Received-SPF: pass (google.com: domain of shakeelb@google.com designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; Authentication-Results: mx.google.com; dkim=pass header.i=@google.com header.s=20161025 header.b=LP65T9uo; spf=pass (google.com: domain of shakeelb@google.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=shakeelb@google.com; dmarc=pass (p=REJECT sp=REJECT dis=NONE) header.from=google.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=cWy39L110bpl90KlTOYN36nnj0m9Og8hXJw1+zoZDKk=; b=LP65T9uo0dVn2Y5omvF5mxvXGRfAgu6NngtzQkPAnlMx95MzRaoxUddWsZp48rD13D DVYmLNGVWFeqmVnvvMAV+nlf+frio4tA488tODN1HVqEvHfhTW5BOunil70RJ/PsIhYE AVgukhQXhJcaGfW/bxdzEpdpiwIo/iM6ZGTv3XE8Y3RuPKBM4A8WyrvK4tDNZUmeWYl9 wLKIa898nv5rY6FJxM+Z2Bz1Tk8gGszZttNaJ7iQfD4v9jr1wIsYMwMZhHPbEWz/2gJT zl199wVxdgncig7ajSNj8hQEX/RicdcdKS2ywd0YJfPSMTtbNXfvLGLH43wX3vF0nHyC CWiA== X-Google-Smtp-Source: APXvYqznZO7Qm/QhFUfHKm3tnghM46ifrr9A348bqIDJYnm/2sGPr6e7rkOfkOAFCHIVkOnCoZYMtWSNR8ycH5WBDbs= X-Received: by 2002:a81:9ad0:: with SMTP id r199mr46915127ywg.310.1555099648342; Fri, 12 Apr 2019 13:07:28 -0700 (PDT) MIME-Version: 1.0 References: <20190412151507.2769-1-hannes@cmpxchg.org> In-Reply-To: <20190412151507.2769-1-hannes@cmpxchg.org> From: Shakeel Butt Date: Fri, 12 Apr 2019 13:07:17 -0700 Message-ID: Subject: Re: [PATCH 0/4] mm: memcontrol: memory.stat cost & correctness To: Johannes Weiner Cc: Andrew Morton , Linux MM , Cgroups , LKML , kernel-team@fb.com Content-Type: text/plain; charset="UTF-8" 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 Fri, Apr 12, 2019 at 8:15 AM Johannes Weiner wrote: > > The cgroup memory.stat file holds recursive statistics for the entire > subtree. The current implementation does this tree walk on-demand > whenever the file is read. This is giving us problems in production. > > 1. The cost of aggregating the statistics on-demand is high. A lot of > system service cgroups are mostly idle and their stats don't change > between reads, yet we always have to check them. There are also always > some lazily-dying cgroups sitting around that are pinned by a handful > of remaining page cache; the same applies to them. > > In an application that periodically monitors memory.stat in our fleet, > we have seen the aggregation consume up to 5% CPU time. > > 2. When cgroups die and disappear from the cgroup tree, so do their > accumulated vm events. The result is that the event counters at > higher-level cgroups can go backwards and confuse some of our > automation, let alone people looking at the graphs over time. > > To address both issues, this patch series changes the stat > implementation to spill counts upwards when the counters change. > > The upward spilling is batched using the existing per-cpu cache. In a > sparse file stress test with 5 level cgroup nesting, the additional > cost of the flushing was negligible (a little under 1% of CPU at 100% > CPU utilization, compared to the 5% of reading memory.stat during > regular operation). For whole series: Reviewed-by: Shakeel Butt > > include/linux/memcontrol.h | 96 +++++++------- > mm/memcontrol.c | 290 +++++++++++++++++++++++++++---------------- > mm/vmscan.c | 4 +- > mm/workingset.c | 7 +- > 4 files changed, 234 insertions(+), 163 deletions(-) > >