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[209.85.220.65]) by mx.google.com with SMTPS id l22sor7708966iob.74.2019.04.02.00.54.45 for (Google Transport Security); Tue, 02 Apr 2019 00:54:45 -0700 (PDT) Received-SPF: pass (google.com: domain of laoar.shao@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=Jp+tSC8K; spf=pass (google.com: domain of laoar.shao@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=laoar.shao@gmail.com; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=fVRLBEFJAHoY/K/5EzGGyJBatAKnecX/Sq5cGdSYc0s=; b=Jp+tSC8KXs59bN3V9va6En1vKRiMgE/EUonl64nULWgG61luh1ha6SbwdKCZEXepZN qoYb4rOUGISKgbtZWVsB+6xA3ivmiqMJkuEtqRIA9ArE9X5e/gCd8hLzsHdrRotPeS/e s0AJdIZ3gRN0FQU7xIXivtcY6zGmC8fpBedeHqHFu6V708FTKY/yAqjCuR1DF2SKKt7p Td7GviYLJOqlfkaojRwJpI6uBcJZQkOq/Tc6tUZ6vwD/z0O0ow40fO8rhH2BKxDpjQY8 zwqTsJ0aHoyMTxvLjSII/8Vn5WTm4T0yiluWkS+1Gjd+tch2uJa4+r5RTbK4C53ITOqC ZB4Q== X-Google-Smtp-Source: APXvYqzsGFuogadboqKMrmzXjrqwss0e7hgtnpNQeT6udYT4CHn1L2tGEFYr80gO3Ldd2aCl2+2o0G7K9NN1bZmZVqY= X-Received: by 2002:a5d:8c98:: with SMTP id g24mr1243535ion.35.1554191685290; Tue, 02 Apr 2019 00:54:45 -0700 (PDT) MIME-Version: 1.0 References: <1554185720-26404-1-git-send-email-laoar.shao@gmail.com> <20190402072351.GN28293@dhcp22.suse.cz> <20190402074459.GP28293@dhcp22.suse.cz> In-Reply-To: <20190402074459.GP28293@dhcp22.suse.cz> From: Yafang Shao Date: Tue, 2 Apr 2019 15:54:09 +0800 Message-ID: Subject: Re: [PATCH] mm: add vm event for page cache miss To: Michal Hocko Cc: willy@infradead.org, Jan Kara , Hugh Dickins , Vlastimil Babka , Andrew Morton , Linux MM 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 Tue, Apr 2, 2019 at 3:45 PM Michal Hocko wrote: > > On Tue 02-04-19 15:38:02, Yafang Shao wrote: > > On Tue, Apr 2, 2019 at 3:23 PM Michal Hocko wrote: > > > > > > On Tue 02-04-19 14:15:20, Yafang Shao wrote: > > > > We found that some latency spike was caused by page cache miss on our > > > > database server. > > > > So we decide to measure the page cache miss. > > > > Currently the kernel is lack of this facility for measuring it. > > > > > > What are you going to use this information for? > > > > > > > With this counter, we can monitor pgcachemiss per second and this can > > give us some informaton that > > whether the database performance issue is releated with pgcachemiss. > > For example, if this value increase suddently, it always cause latency spike. > > > > What's more, I also want to measure how long this page cache miss may cause, > > but this seems more complex to implement. > > Aren't tracepoints a better fit with this usecase? You not only get the > count of misses but also the latency. Btw. latency might be caused also > for the minor fault when you hit lock contention. > > I have think about tracepoints before, the reason why I don't choose it is that the implementation is a little more complex. I will rethinking it. > > > > > > This patch introduces a new vm counter PGCACHEMISS for this purpose. > > > > This counter will be incremented in bellow scenario, > > > > - page cache miss in generic file read routine > > > > - read access page cache miss in mmap > > > > - read access page cache miss in swapin > > > > > > > > NB, readahead routine is not counted because it won't stall the > > > > application directly. > > > > > > Doesn't this partially open the side channel we have closed for mincore > > > just recently? > > > > > > > Seems I missed this dicussion. > > Could you pls. give a reference to it? > > The long thread starts here http://lkml.kernel.org/r/nycvar.YFH.7.76.1901051817390.16954@cbobk.fhfr.pm > -- > Michal Hocko > SUSE Labs