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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> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 2E79320002 X-Rspam-User: X-Stat-Signature: nceq5uh51j6mp9u3853atq9n4dozmtqf X-HE-Tag: 1781897170-994611 X-HE-Meta: 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 CbswXpPD Hl6gtAM4T+duWSNxzTM/+A6YFy/o4/hGlQuxhrTwdXHIyzUWalj6cGvMzhMWL851agPf1xqOo2N0VKSVhNYNA5f5B54Mw3LBNnpN2wCBSJ7DdZCt6YVswte9HzGjh6UKsYOuimazNbhMIHXVdfIv+g55OPa2xIkJ3OuC24kVwXtj+yin2nJM/b+qFNsR7AkdED87YnW7k56ETEMlvhwlDX6IRYHKkUbBCwQsJm9pL/N01ZsWYh1SrPC1ACwDp+Bsf1PzwswZysWPpGkEGgIT423HWk85wF/12PTQ2MNsUIw7R2fi7gr2oPO/h0XLbVUVGzrGAQfgJLT7nngPtZKI7/xOyt/LdVdkZdMsc2FcaGzZk+Ka0DtmjZc0ILgETOt51RM4F0X1Rb6DwtiQ= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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