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Received: from willy by casper.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1vpqa9-0000000BKsu-2Izr; Tue, 10 Feb 2026 16:27:21 +0000 Date: Tue, 10 Feb 2026 16:27:21 +0000 From: Matthew Wilcox To: Dev Jain Cc: akpm@linux-foundation.org, david@kernel.org, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, ryan.roberts@arm.com, anshuman.khandual@arm.com, kirill@shutemov.name Subject: Re: [PATCH] mm: map maximum pages possible in finish_fault Message-ID: References: <20260206135648.38164-1-dev.jain@arm.com> <397482e7-3c89-48e5-9e8c-0798ac92cc05@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <397482e7-3c89-48e5-9e8c-0798ac92cc05@arm.com> X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 0AA6C140002 X-Stat-Signature: cay9xu1obzrjhjfxi81qqrzdhnhs3h8f X-Rspam-User: X-HE-Tag: 1770740850-512747 X-HE-Meta: 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 i6oFdFN+ FJWOIZBCzTOBf3UmS3rOJT5RoxJJofhzxBtVrbRCwaDnPaeiOOWwysF3O6qVTEulnw1DgHLpo4M+i7EUOdHszb8cGbiC/g+W4mmxQ5J0ME4YO0UPYB3uzG+nSm1mXHQ+WmsWH1h2vQOOP1R16Zr6bziqj03DMCDi/eFOQsl77H820MhMzoEM2DL1OWazdeXaSfdfrN089qsZf5xtRY92wgSwrLmr4sA3iFi90fXG2xRoVwdMYrTnmvtF0WJk5Z/kBhs2TpwhC3S/UGHkofco8E8rJk8XEHNKMUDrtH+6CYpSblmI= 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 Tue, Feb 10, 2026 at 06:58:37PM +0530, Dev Jain wrote: > On 06/02/26 8:52 pm, Matthew Wilcox wrote: > > It's nice that you can construct a test-case that shows improvement, but > > is there any real workload that benefits from this? > > I can try to measure this. But, I constructed that testcase to test the > code path, not to show a perf boost (although the boost is obvious enough > so why not show it). As I say in the description: > > "Align finish_fault with filemap_map_pages, and map as many pages as > possible, without crossing VMA/PMD/file boundaries." > > The patch should rather be seen as an extension to 19773df031bc > ("mm/fault: try to map the entire file folio in finish_fault()"). > The code which my patch removes, was added when the norm was to still > perform per-page fault, the argument being, RSS inflation. > > Perhaps I can polish the patch description so that it clearly mentions > what the objective is. You say "removing code". Diffstat says "no real difference in amount of code". 1 file changed, 38 insertions(+), 34 deletions(-) You're messing with some complex code and you haven't said why it's important for us to spend effort making sure you haven't made a mistake. Please persuade us that this is worth doing.