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Thu, 27 Feb 2020 22:53:06 -0800 (PST) Received: from js1304-desktop ([114.206.198.176]) by smtp.gmail.com with ESMTPSA id b3sm9829932pft.73.2020.02.27.22.53.03 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 27 Feb 2020 22:53:05 -0800 (PST) Date: Fri, 28 Feb 2020 15:52:59 +0900 From: Joonsoo Kim To: Aaron Lu Cc: Johannes Weiner , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Michal Hocko , Hugh Dickins , Minchan Kim , Vlastimil Babka , Mel Gorman , kernel-team@lge.com Subject: Re: [PATCH v2 0/9] workingset protection/detection on the anonymous LRU list Message-ID: <20200228065214.GA17349@js1304-desktop> References: <1582175513-22601-1-git-send-email-iamjoonsoo.kim@lge.com> <20200226193942.30049da9c090b466bdc5ec23@linux-foundation.org> <20200227134806.GC39625@cmpxchg.org> <20200228032358.GB634650@ziqianlu-desktop.localdomain> <20200228040214.GA21040@js1304-desktop> <20200228055726.GA674737@ziqianlu-desktop.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200228055726.GA674737@ziqianlu-desktop.localdomain> User-Agent: Mutt/1.5.24 (2015-08-30) 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, Feb 28, 2020 at 01:57:26PM +0800, Aaron Lu wrote: > On Fri, Feb 28, 2020 at 01:03:03PM +0900, Joonsoo Kim wrote: > > Hello, > > > > On Fri, Feb 28, 2020 at 11:23:58AM +0800, Aaron Lu wrote: > > > On Thu, Feb 27, 2020 at 08:48:06AM -0500, Johannes Weiner wrote: > > > > On Wed, Feb 26, 2020 at 07:39:42PM -0800, Andrew Morton wrote: > > > > > It sounds like the above simple aging changes provide most of the > > > > > improvement, and that the workingset changes are less beneficial and a > > > > > bit more risky/speculative? > > > > > > > > > > If so, would it be best for us to concentrate on the aging changes > > > > > first, let that settle in and spread out and then turn attention to the > > > > > workingset changes? > > > > > > > > Those two patches work well for some workloads (like the benchmark), > > > > but not for others. The full patchset makes sure both types work well. > > > > > > > > Specifically, the existing aging strategy for anon assumes that most > > > > anon pages allocated are hot. That's why they all start active and we > > > > then do second-chance with the small inactive LRU to filter out the > > > > few cold ones to swap out. This is true for many common workloads. > > > > > > > > The benchmark creates a larger-than-memory set of anon pages with a > > > > flat access profile - to the VM a flood of one-off pages. Joonsoo's > > > > > > test: swap-w-rand-mt, which is a multi thread swap write intensive > > > workload so there will be swap out and swap ins. > > > > > > > first two patches allow the VM to usher those pages in and out of > > > > > > Weird part is, the robot says the performance gain comes from the 1st > > > patch only, which adjust the ratio, not including the 2nd patch which > > > makes anon page starting from inactive list. > > > > > > I find the performance gain hard to explain... > > > > Let me explain the reason of the performance gain. > > > > 1st patch provides more second chance to the anonymous pages. > > By second chance, do I understand correctely this refers to pages on > inactive list get moved back to active list? Yes. > > > In swap-w-rand-mt test, memory used by all threads is greater than the > > amount of the system memory, but, memory used by each thread would > > not be much. So, although it is a rand test, there is a locality > > in each thread's job. More second chance helps to exploit this > > locality so performance could be improved. > > Does this mean there should be fewer vmstat.pswpout and vmstat.pswpin > with patch1 compared to vanilla? It depends on the workload. If the workload consists of anonymous pages only, I think, yes, pswpout/pswpin would be lower than vanilla with patch #1. With large inactive list, we can easily find the frequently referenced page and it would result in less swap in/out. Thanks.