From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 44879606A31B for ; Wed, 4 Nov 2026 17:15:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=h/WBm7u6 Received: by kanga.kvack.org (Postfix) id 4DB1D6B05B3; Wed, 4 Nov 2026 12:15:21 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 4B46C6B05B7; Wed, 4 Nov 2026 12:15:21 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 3CFA46B05B3; Wed, 4 Nov 2026 12:15:21 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 1B2236B05B3 for ; Wed, 4 Nov 2026 12:15:21 -0500 (EST) Received: from smtpin29.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay06.hostedemail.com (Postfix) with ESMTP id A585AA8453 for ; Wed, 4 Nov 2026 17:15:20 +0000 (UTC) X-FDA: 85398087600.29.68B83CC Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf13.hostedemail.com (Postfix) with ESMTP id DDE4420013 for ; Wed, 4 Nov 2026 17:15:18 +0000 (UTC) Authentication-Results: imf13.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b="h/WBm7u6"; spf=pass (imf13.hostedemail.com: domain of ljs@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=ljs@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1793812518; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=SYq9+BBr0q0gADHtUh7wcOV25vq3s2GgCZsPxG2VA6Q=; b=MSyL2bpaeThg/Sm35/qx93kWDKU7ueeHWXZDgXP5yjRJm2Rpp7Sthx8EWZhXjbzxw14npv dWVcmwX/a9hM8+6t4U183OJmV26o196SJmxkR787Oczi0hO1nx4eMHmk+zdayBewS8MGRY OK0HFdytWAkDNyhTAj5ySQEd2+eZmyU= ARC-Authentication-Results: i=1; imf13.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b="h/WBm7u6"; spf=pass (imf13.hostedemail.com: domain of ljs@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=ljs@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1793812518; b=iM8IgXUBz2+/mhgALYb+9bQ25SJ4RFHwXsSBD5AfSvDVRlLnP9vBx8peqAQnftGVRrDcB6 0DHK8OyWXte0K5fhHU4ocyp3SwBMlegyokQiBx+pg03dWLXIyZI+JVtGDENAYi3dNpRPZ4 2oFamKWS4LcvYmYZKV8xIrDl/Zcg4bk= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 22F016021C; Wed, 4 Nov 2026 17:15:18 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4B3671F00919; Wed, 4 Nov 2026 17:15:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793812517; bh=SYq9+BBr0q0gADHtUh7wcOV25vq3s2GgCZsPxG2VA6Q=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=h/WBm7u6jgGnIGCnazSx+mTpGGIdY44Edu9dfObP1hyHC87oXtWB0MMAm4MFUJJ/u lBTy/MMP0imnbuTtYVYfUthcWkCCJps5xV7IEhakoied3Y/YAYJ2LCW19zBAqJx4pH sESid7Gte1+yneVlzgi9FxomuyS5X741ccgnYFFmh/GqG+xRbGnDTzIU15SABc9zUT En1QWKFCENGlbrm4Vqm2JURpdLhBKzYNmXQLpTfEcInf5v26cvGepdDB33FjMahU29 zYFvvfTS0M08OkXL5giLs6Lh5R2qjGs5WvxH+v452VLnqRD8w0FarnxUqHIsZr2Eln lZUSab8BSMMHg== Date: Wed, 4 Nov 2026 17:15:10 +0000 From: "Lorenzo Stoakes (ARM)" To: Pedro Falcato Cc: Pranith Kumar , "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-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Stat-Signature: fzo11dsrzy58ijkf8mmn84ghux7nr1wm X-Rspamd-Server: rspam01 X-Rspam-User: X-Spam-Status: No, score=-5.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS autolearn=no autolearn_force=no version=4.0.1 X-Rspamd-Queue-Id: DDE4420013 X-HE-Tag: 1793812518-961616 X-HE-Meta: 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 v/W9fsbq dpLptSoW30PSZGhyCyqCd8t3OsoTlOnbPmhRh6dpmTX9nvfMhrLRWq6ZXZD7rjDrvz1C/8aGYV4jhPQS8gVMofZb+SLLE7fqz2xIpucIssXXfbK64C8CXSB4WpRGGFZqAjXW+lSDfsDorXqE0nGmnS1vCCthnRY5ZqOoP4zud3AjYhTCVk0GELMWIWaKqlBlRAZQ/b1xhXDDtFnbbZrRdBXTwNsGS7W2WL30kNfrB+DKRArJxHgi/R3I/D9yDOXtdwQeM87cQD/qr//KSD50lU8mcvIC42/TWQ4mkXzmllrY0P0443qE9ZP4KzgGv6iRof8kb2PujAHYQkkomdrE3f5XpkPt6sS+DXrGZOAOJRz3YYm8+fnb5YX37Vg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Wed, Nov 04, 2026 at 05:08:10PM +0000, Pedro Falcato wrote: > 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. Exactly. > > > > > > > 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 All of it? Your commit message simply asserts that this is true. > > 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. Exactly. And this patch boldly decides to CHANGE the invariant here without evidence for a theorised perf gain. Sorry we don't have time for this. NAK. -- Cheers, Lorenzo