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Wed, 4 Nov 2026 17:08:12 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id wvMBFHxm62pTFgAAD6G6ig (envelope-from ); Wed, 04 Nov 2026 17:08:12 +0000 Date: Wed, 4 Nov 2026 17:08:10 +0000 From: Pedro Falcato To: Pranith Kumar Cc: "Lorenzo Stoakes (ARM)" , "David Hildenbrand (Arm)" , Andrew Morton , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Rik van Riel , Harry Yoo , Jann Horn , Lance Yang , Richard Cochran , "open list:MEMORY MANAGEMENT - CORE" , open list , "open list:PTP HARDWARE CLOCK SUPPORT:Keyword:(?:b|_)ptp(?:b|_)" Subject: Re: [RFC PATCH] mm/rmap: use release ordering for small-folio mapcount removal Message-ID: References: <20261104013139.1341582-1-bobby.prani@gmail.com> <750560f3-4c5a-44fe-b72a-0611be383f32@kernel.org> <287698ab-76dc-4aee-8e6c-db1f5d18974c@kernel.org> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Spam-Flag: NO X-Spam-Level: X-Spamd-Result: default: False [-11.80 / 50.00]; SUSE_INTERNAL_BYPASS(-9.00)[]; BAYES_HAM(-3.00)[100.00%]; SUSPICIOUS_RECIPS(1.50)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; TO_DN_ALL(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; ARC_NA(0.00)[]; FREEMAIL_TO(0.00)[gmail.com]; MIME_TRACE(0.00)[0:+]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; RCVD_TLS_ALL(0.00)[]; RCPT_COUNT_TWELVE(0.00)[17]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; FREEMAIL_CC(0.00)[kernel.org,linux-foundation.org,infradead.org,google.com,suse.com,surriel.com,linux.dev,gmail.com,kvack.org,vger.kernel.org]; RCVD_COUNT_TWO(0.00)[2]; RCVD_VIA_SMTP_AUTH(0.00)[]; TAGGED_RCPT(0.00)[]; MISSING_XM_UA(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo] X-Spam-Score: -11.80 On Wed, Nov 04, 2026 at 08:51:20AM -0800, Pranith Kumar wrote: > Hi Lorenzo, > > On Wed, Nov 4, 2026 at 5:55 AM Lorenzo Stoakes (ARM) wrote: > > > > On Wed, Nov 04, 2026 at 02:37:39PM +0100, David Hildenbrand (Arm) wrote: > > > > I mean 1.54%, theoretically is even less convincing for me :) > > With reducing the strength of one barrier, I think this is a non-trivial gain. Counting cycles on an arm64 simulator for a microbenchmark is completely unconvincing. > > > > In any case for something touching a sensitive memory barrier operation to have > > a stronger argument put forward for release ordering being suitable than simply > > stating it's fine in the commit message and updating a comment. > > > > Can you please explain what information is missing? I think the commit > message has all the details of why release is sufficient instead of > full barrier. rmap is gnarly code and I'm not sure people have an appetite towards weakening random atomic ordering semantics for a virtual 1.54% cycles gain in some microbenchmark, without actually explaining why it is safe. __folio_remove_rmap() has (indirectly) a lot of callers which may subtly expect different semantics. -- Pedro