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Fri, 19 Jun 2026 19:26:06 +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 gPtPLs6XNWo4OwAAD6G6ig (envelope-from ); Fri, 19 Jun 2026 19:26:06 +0000 Date: Fri, 19 Jun 2026 20:26:05 +0100 From: Pedro Falcato To: Suren Baghdasaryan Cc: Matthew Wilcox , Lorenzo Stoakes , Andrew Morton , Frederick Mayle , Kalesh Singh , Jan Kara , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, David Hildenbrand Subject: Re: [PATCH mm-hotfixses] Revert "mm: limit filemap_fault readahead to VMA boundaries" Message-ID: References: <20260619112852.104213-1-ljs@kernel.org> <20260619093711.d0d37c9920b3a16394c356a6@linux-foundation.org> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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-Score: -4.30 X-Spamd-Result: default: False [-4.30 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; ARC_NA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; MISSING_XM_UA(0.00)[]; MIME_TRACE(0.00)[0:+]; FUZZY_RATELIMITED(0.00)[rspamd.com]; RCPT_COUNT_SEVEN(0.00)[11]; RCVD_TLS_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; DBL_BLOCKED_OPENRESOLVER(0.00)[infradead.org:email,imap1.dmz-prg2.suse.org:helo,pedro-suse.lan:mid] X-Spam-Level: On Fri, Jun 19, 2026 at 10:52:07AM -0700, Suren Baghdasaryan wrote: > On Fri, Jun 19, 2026 at 10:46 AM Matthew Wilcox wrote: > > > > On Fri, Jun 19, 2026 at 10:43:06AM -0700, Suren Baghdasaryan wrote: > > > > Yeah, the mmap usage on SVT-AV1 is a little suspicious, but I guess the > > > > pattern may come up time and time again for people doing chunked mmap > > > > reads. I think we need to take a closer look at this change. > > > > > > Frame-by-frame mmapping for a streaming workoad is quite questionable > > > IMHO and I don't think we should be optimizing or encouraging such > > > usage, but I understand the reasoning for the revert. > > > > If userspace is properly tuned, it doesn't need automatic readahead > > at all; it can disable it and issue manual readaheads. The point of > > automatic readahead is to cope with userspace which is doing stupid > > things like calling read() for a single byte at a time. > > > > Could it have better defaults? Maybe! It's worth a try. But those > > attempts need to have a very low bar for reversion when it turns out > > they affect other workloads. > > That what I meant in the last part of my reply :) > > But in general, I think that benchmark measuring "how many frames per > second a CPU can encode" should be revised so it doesn't depend on > file prefetching mechanisms. Otherwise it's measuring something else. To be clear, that's not (necessarily) a benchmark, the code we were looking at is their encoder app. (it's also generally not possible to prefetch the whole thing into RAM because, well, raw video files are quite large) -- Pedro