From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 880EACD4F26 for ; Fri, 19 Jun 2026 17:07:40 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 6DE636B008A; Fri, 19 Jun 2026 13:07:39 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 68F436B008C; Fri, 19 Jun 2026 13:07:39 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 558D76B0092; Fri, 19 Jun 2026 13:07:39 -0400 (EDT) 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 30D8C6B008A for ; Fri, 19 Jun 2026 13:07:39 -0400 (EDT) Received: from smtpin24.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay06.hostedemail.com (Postfix) with ESMTP id A00251C4FBC for ; Fri, 19 Jun 2026 17:07:38 +0000 (UTC) X-FDA: 84897293796.24.A437206 Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf20.hostedemail.com (Postfix) with ESMTP id ED4B11C0003 for ; Fri, 19 Jun 2026 17:07:36 +0000 (UTC) Authentication-Results: imf20.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=brkFo1gg; spf=pass (imf20.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=1781888857; b=FRh07K6wHjnhC7U6KYIGkWKhnUDCZzUf2xqLf3P0ZSD44Zl5k5NU79Xh0rvsTcH+hH6PUj Pd0ItF4pguFeuQdAQl83voRsMqn6IcPdI3pAsfb9xVE1Bpiw4dTP/lx0EIATokfMw5pdiy G/e/OmP1suXKhNCRH3wLrUnbqL9Y1kg= ARC-Authentication-Results: i=1; imf20.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=brkFo1gg; spf=pass (imf20.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=1781888856; 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: in-reply-to:in-reply-to:references:references:dkim-signature; bh=aeuB26U0brIWccqtcDGehQkxyCwlFMLLMddYu0942Iw=; b=w90+t8AdWWvMqCPGyetacEb/h1J2WuVJc5lDfg3Z3ywgsWRkU6HnJi4AucTEdOZ5xQKSnZ H8NZ7l5O4mVJCdCDyh2ISkZaftE+ve/6ZMf3TD+Jd6IC7DgdLH6GGbZQTeJgvB6VNI+90O WlRuRD3ihot2ZO2+9VAm7WNHb5JDfGo= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 56D2C601E1; Fri, 19 Jun 2026 17:07:36 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 90E131F000E9; Fri, 19 Jun 2026 17:07:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781888856; bh=aeuB26U0brIWccqtcDGehQkxyCwlFMLLMddYu0942Iw=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=brkFo1ggwWjEhDRsLhYJemXNMQkQUusqJmybB7qBNJ4XDdafvDSJQKrUxjm7GFIvF tbjbdOhaMOjEc7KzbMFOKfJkEwRbp9IgRt+j0TLFlcACCSahsJsC1TKGj/LLQTHWma ERYxbv7aIel7FiBSISmkvZhd/h2/Bvvf/pvy7Yww5kPmq5CyTThIcM+KOkyqFwz5mZ ZjQdyvNSThJcniisREZm6Iu7/AbIXR5cGATSV4hJ+KQ8ZVmowIAUNKZBcYfXQEMEKm /H2RKK1IiyM12fU7/tQDhVcOasb2rVyqmltwOvmyHiueChRLjggZrNkmLCkRQiMFVZ GPlll8wVbh2bA== Date: Fri, 19 Jun 2026 18:07:30 +0100 From: Lorenzo Stoakes To: Matthew Wilcox Cc: Andrew Morton , Frederick Mayle , Kalesh Singh , Jan Kara , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Suren Baghdasaryan , Pedro Falcato , 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=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: ED4B11C0003 X-Stat-Signature: cyi5rbs8f9shp3p7h67wjtj7rrwq9y1p X-HE-Tag: 1781888856-868330 X-HE-Meta: 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 8RJl7nI5 iYa/Mmh1ltNWq1TL0Ss0HekA0Us+FCKCqqAIfx5+AN48MZIb9DSUxYXr+x+9SGj3v/Q9/B9cGFjQ3esO+D9603p5JAgKT1dugjSNsBh6JJxPLGXW7jhJPla4wFDx8hUntcPAn/lUsASt1DR6f+DLQlTJ3xNAylmn4rQ9iMhmGrlh08yZwBHzpecTmNhnMc7ii2Uz9agYtVqPaeRp/dV8vNm9lWxkLUFQUqw4zuNoaDIuU6suVHfbGs9kjVb7XWXHjFoo85kot83uveWbeCKIMLUq785HQLrumcTEPuIPNe1qNclnyQTOsDExta/Ha+3BzjbZJFyU2E6WCEiHxWcAzGKsWFA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: +cc Suren, Pedro, David - I messed up the cc on this patch. On Fri, Jun 19, 2026 at 05:52:38PM +0100, Matthew Wilcox wrote: > On Fri, Jun 19, 2026 at 09:37:11AM -0700, Andrew Morton wrote: > > On Fri, 19 Jun 2026 12:28:51 +0100 Lorenzo Stoakes wrote: > > > > > This reverts commit 7b32f64bc512b40b268776c5ac4d354b325b3197. > > > > > > This patch caused a significant performance regression, so revert it, and > > > we can determine whether the approach is sensible or not moving forwards, > > > and if so how to avoid this. > > > > > > There was a merge conflict with commit de97ae6222c1 ("mm/readahead: no > > > PG_readahead on EOF"), care was taken to ensure that the revert retained the > > > behaviour of this patch and cleanly reverts commit 7b32f64bc512 ("mm: limit > > > filemap_fault readahead to VMA boundaries") only. > > > > I'm a little conflicted here. > > > > 7b32f64bc512 avoided readahead of "file pages outside the mapped > > region", which is clearly desirable (arguably a bug fix?) and we care I wouldn't say it's a bug fix? The kernel has always done this with no reported bugs. > > about performance of executable mappings. Whereas it isn't clear that > > we care about whatever the heck that test case was doing. > > > > IOW, the revert might make the kernel worse, overall. > > > > If someone plans to get down and analyse that test case then come up > > with a new version of 7b32f64bc512 then OK. Is there such a person? > > > > I'll park the revert in mm-unstable for now, but would prefer not to > > rush it in until we better understand what's going on with that test > > case and what can be done to address it. As Willy points out [0], we've identified that it's a real usecase that we're regressing. There's likely others too in the real world. This approach has also not been without debate in the past (see [1]), I think this patch slipped under the radar on that front a bit. So yeah, this does not to be reverted, and as a hotfix sooner rather than later. > > Suren did that work. > https://lore.kernel.org/linux-mm/CAJuCfpH_Fp=J-m-kVZ3VVmqH0cAfNX6CQKWt3XmAJq1Rp9sFwQ@mail.gmail.com/ Thanks for highlighting that Willy (copied -> [0]). Overall, if a patch causes a major regression in a core mm subsystem, people can wait a cycle to re-evaluate. Thanks, Lorenzo [0]:https://lore.kernel.org/linux-mm/CAJuCfpH_Fp=J-m-kVZ3VVmqH0cAfNX6CQKWt3XmAJq1Rp9sFwQ@mail.gmail.com/ [1]:https://lore.kernel.org/linux-mm/CAC_TJvfG8GcwG_2w1o6GOTZS8tfEx2h9A91qsenYfYsX8Te=Bg@mail.gmail.com/