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Wed, 25 Jan 2023 14:21:37 -0800 (PST) Received: from google.com ([2620:15c:211:201:4ff6:fb01:3677:2696]) by smtp.gmail.com with ESMTPSA id x12-20020aa793ac000000b005898fcb7c2bsm4277118pff.170.2023.01.25.14.21.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 25 Jan 2023 14:21:37 -0800 (PST) Date: Wed, 25 Jan 2023 14:21:35 -0800 From: Minchan Kim To: Michal Hocko Cc: Andrew Morton , Suren Baghdasaryan , Matthew Wilcox , linux-mm , LKML Subject: Re: [PATCH v2] mm/madvise: add vmstat statistics for madvise_[cold|pageout] Message-ID: References: <20230125005457.4139289-1-minchan@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 08E48C0015 X-Stat-Signature: t1hhzwt9kt7nameo1p6b779wnatu6kp5 X-HE-Tag: 1674685298-186727 X-HE-Meta: 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 /KZx+eNa e9s4txLZJo2Fv6mJClKf1s/dnxW7F0y5RjOsZ55yMcgDovQ7RKpVksvLHTOJfLDzRdXUqG3oQEpe3D33c6LFwl35Ca/SR+Q7YzaDK6tKAWV3+ywCECljPmkx2wwdeWsFPK17v0CnuF4zhbPw0cUB9LovK5aIkZYzHHZMyK9OnGHCNr5yHU1NgYEqN80qKcrXXql96BLhSC2qXkFTzdVAC0ooImQuVscPZsa/UUa8XTzzJIsZo6QcLgueztpsimMdu8DLsqwtoEzGm+JSr+rF7LADoUfPGJqForH0k1O05y2Tz4IZwNpTqE2Xj9lKgUHJWgznukJga5AyBZEQzCreH2oCRphDYlqVDT4q2wAXUfdpIJICs0vlUnT8mWHpNZXlC38tZ5WwlTY/9Aa8gEr+CrR97L16+F0ECq4207BBY2bHcyao5vLuNejhKVITAQJfj5RyzhXbQRqr2nbjZ4eGgqrdKHIeTj5DOn3N/D6aRIbtT/kY8bn7i5dHT0CWWqq13SIBtYBi0BiapnZpkQ3IQQ2kJV27SXoMVgJijqQ+gIvrefhaIPn6G50eGD9i4QCZ+RU9/U9434TY5KPPYoUZ9ZkXy2BU9Poe0OnUb 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, Jan 25, 2023 at 10:37:59PM +0100, Michal Hocko wrote: > On Wed 25-01-23 10:07:49, Minchan Kim wrote: > > On Wed, Jan 25, 2023 at 06:07:00PM +0100, Michal Hocko wrote: > > > On Wed 25-01-23 08:36:02, Minchan Kim wrote: > > > > On Wed, Jan 25, 2023 at 09:04:16AM +0100, Michal Hocko wrote: > > > > > On Tue 24-01-23 16:54:57, Minchan Kim wrote: > > > > > > madvise LRU manipulation APIs need to scan address ranges to find > > > > > > present pages at page table and provides advice hints for them. > > > > > > > > > > > > Likewise pg[scan/steal] count on vmstat, madvise_pg[scanned/hinted] > > > > > > shows the proactive reclaim efficiency so this patch adds those > > > > > > two statistics in vmstat. > > > > > > > > > > > > madvise_pgscanned, madvise_pghinted > > > > > > > > > > > > Since proactive reclaim using process_madvise(2) as userland > > > > > > memory policy is popular(e.g,. Android ActivityManagerService), > > > > > > those stats are helpful to know how efficiently the policy works > > > > > > well. > > > > > > > > > > The usecase description is still too vague. What are those values useful > > > > > for? Is there anything actionable based on those numbers? How do you > > > > > deal with multiple parties using madvise resp. process_madvise so that > > > > > their stats are combined? > > > > > > > > The metric helps monitoing system MM health under fleet and experimental > > > > tuning with diffrent policies from the centralized userland memory daemon. > > > > > > That is just too vague for me to imagine anything more specific then, we > > > have numbers and we can show them in a report. What does it actually > > > mean that madvise_pgscanned is high. Or that pghinted / pgscanned is > > > low (that you tend to manually reclaim sparse mappings)? > > > > If that's low, it means the userspace daemon's current tune/policy are > > inefficient or too aggressive since it is working on address spacess > > of processes which don't have enough memory the hint can work(e.g., > > shared addresses, cold address ranges or some special address ranges like > > VM_PFNMAP) so sometime, we can detect regression to find culprit or > > have a chance to look into better ideas to improve. > > Are you sure this is really meaningful metric? Just consider a large and > sparsely populated mapping. This can be a perfect candidate for user > space reclaim target (e.g. consider a mapping covering a large matrix > or other similar data structure). pghinted/pgscanned would be really > small while the reclaim efficiency could be quite high in that case, > wouldn't it? Why do you think it's efficient? It need to spend quite CPU cycle to scan a few of pages to evict. I don't see it's efficient if it happens quite a lot.