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imf28.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=arm.com; spf=pass (imf28.hostedemail.com: domain of dev.jain@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=dev.jain@arm.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1770731707; a=rsa-sha256; cv=none; b=Y7De0XRw7FZCgYTc5MMuxn61YFb+G7DInjaqMc5q5sYuKaIP3SE6rQO9dEkfxyGInNNBNf +E/9x8alyc2wbQQrzFnq64WVK2Uem2ij7dx9j0u7TmmDaDpZZGRGqlHGUdKOzdsKFhP1EY kx4ftrD7yYcym0UM6k5HxJGdfCGBJYI= Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 54228339; Tue, 10 Feb 2026 05:55:00 -0800 (PST) Received: from [10.164.19.61] (unknown [10.164.19.61]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 455553F632; Tue, 10 Feb 2026 05:55:01 -0800 (PST) Message-ID: Date: Tue, 10 Feb 2026 19:24:59 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: map maximum pages possible in finish_fault To: Lorenzo Stoakes Cc: Matthew Wilcox , akpm@linux-foundation.org, david@kernel.org, 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 References: <20260206135648.38164-1-dev.jain@arm.com> <397482e7-3c89-48e5-9e8c-0798ac92cc05@arm.com> <0c956b6c-1d75-48f0-b55c-ae9887dce79f@lucifer.local> Content-Language: en-US From: Dev Jain In-Reply-To: <0c956b6c-1d75-48f0-b55c-ae9887dce79f@lucifer.local> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: rpnwfa9eeh8xrmbc3h56c544qurjoekf X-Rspamd-Queue-Id: A1DC4C0002 X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1770731707-555636 X-HE-Meta: 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 VmYzeKZs p5EHqRuuzjr4WQq8t+SPOtMD302itCnTDjWSAm9YU42l7k/tvOobsAYQ7vuO2pQrXA+tHRa9ZqA1IbJ0Cy4b2Y5nfEJBrzDUWdsJFPPSwNnHCQrEKcUoacMfy1TeC8c6C2242SELS52qPsLoOqVk4KL4CNLga5ZgtEqa5PNXOtddTS6GZ4ozBJ+yPKNRu53+km58Y 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 10/02/26 7:09 pm, Lorenzo Stoakes wrote: > On Tue, Feb 10, 2026 at 06:58:37PM +0530, Dev Jain wrote: >> On 06/02/26 8:52 pm, Matthew Wilcox wrote: >>> On Fri, Feb 06, 2026 at 07:26:48PM +0530, Dev Jain wrote: >>>> We test the patch with the following userspace program. A shmem VMA of >>>> 2M is created, and faulted in, with sysfs setting >>>> hugepages-2048k/shmem_enabled = always, so that the pagecache is populated >>>> with a 2M folio. Then, a 64K VMA is created, and we fault on each page. >>>> Then, we do MADV_DONTNEED to zap the pagetable, so that we can fault again >>>> in the next iteration. We measure the accumulated time taken during >>>> faulting the VMA. >>>> >>>> On arm64, >>>> >>>> without patch: >>>> Total time taken by inner loop: 4701721766 ns >>>> >>>> with patch: >>>> Total time taken by inner loop: 516043507 ns >>>> >>>> giving a 9x improvement. >>> 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. >> > Can we make any new respin of this RFC please. I am especially not > confident given the immediate syzbot etc. Sure. > > If it's a speculative thing without great justification the series should > be RFC until such time the community decides it's worthwhile. > > Thanks, Lorenzo