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Wed, 04 Jun 2025 05:00:17 -0700 (PDT) Date: Wed, 4 Jun 2025 08:00:13 -0400 From: Johannes Weiner To: Barry Song <21cnbao@gmail.com> Cc: Matthew Wilcox , Lorenzo Stoakes , Andrew Morton , Shakeel Butt , "Liam R . Howlett" , David Hildenbrand , Vlastimil Babka , Jann Horn , Arnd Bergmann , Christian Brauner , SeongJae Park , Usama Arif , Mike Rapoport , linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, Pedro Falcato Subject: Re: [DISCUSSION] proposed mctl() API Message-ID: <20250604120013.GA1431@cmpxchg.org> References: <85778a76-7dc8-4ea8-8827-acb45f74ee05@lucifer.local> <20250529211423.GA1271329@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: CB37180005 X-Stat-Signature: xr57sqgfj5bkpocidneq8h3h4egeuuag X-Rspam-User: X-HE-Tag: 1749038420-871907 X-HE-Meta: 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 r4bbxMUy 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 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: List-Subscribe: List-Unsubscribe: On Fri, May 30, 2025 at 07:52:28PM +1200, Barry Song wrote: > On Fri, May 30, 2025 at 9:14 AM Johannes Weiner wrote: > > > > On Thu, May 29, 2025 at 04:28:46PM +0100, Matthew Wilcox wrote: > > > Barry's problem is that we're all nervous about possibly regressing > > > performance on some unknown workloads. Just try Barry's proposal, see > > > if anyone actually compains or if we're just afraid of our own shadows. > > > > I actually explained why I think this is a terrible idea. But okay, I > > tried the patch anyway. > > > > This is 'git log' on a hot kernel repo after a large IO stream: > > > > VANILLA BARRY > > Real time 49.93 ( +0.00%) 60.36 ( +20.48%) > > User time 32.10 ( +0.00%) 32.09 ( -0.04%) > > System time 14.41 ( +0.00%) 14.64 ( +1.50%) > > pgmajfault 9227.00 ( +0.00%) 18390.00 ( +99.30%) > > workingset_refault_file 184.00 ( +0.00%) 236899.00 (+127954.05%) > > > > Clearly we can't generally ignore page cache hits just because the > > mmaps() are intermittent. > > Hi Johannes, > Thanks! > > Are you on v1, which lacks folio demotion[1], or v2, which includes it [2]? > > [1] https://lore.kernel.org/linux-mm/20250412085852.48524-1-21cnbao@gmail.com/ > [2] https://lore.kernel.org/linux-mm/20250514070820.51793-1-21cnbao@gmail.com/ The subthread is about whether the reference dismissal / demotion should be unconditional (v1) or opt-in (v2). I'm arguing for v2.