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 CE23ACD37AC for ; Fri, 8 May 2026 23:53:49 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id C8EDF6B02BF; Fri, 8 May 2026 19:53:48 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id C66806B02C1; Fri, 8 May 2026 19:53:48 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id BA3716B02C2; Fri, 8 May 2026 19:53:48 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id ABE9D6B02BF for ; Fri, 8 May 2026 19:53:48 -0400 (EDT) Received: from smtpin08.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay05.hostedemail.com (Postfix) with ESMTP id 3E13040423 for ; Fri, 8 May 2026 23:53:48 +0000 (UTC) X-FDA: 84745907736.08.B6B273B Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf15.hostedemail.com (Postfix) with ESMTP id A2169A0002 for ; Fri, 8 May 2026 23:53:46 +0000 (UTC) Authentication-Results: imf15.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=korg header.b=FyXfE1Bw; dmarc=none; spf=pass (imf15.hostedemail.com: domain of akpm@linux-foundation.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1778284426; 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=xtERP+6axMTYS4b6V07rZTRptsgU9hi1uWfhKjMa5ew=; b=tbC+N4P/F+WauyRb6LNADSJtjqN7MbMeXU0ilZUDVn1OvricOZFTacqnfKQd+gW8Ap36SF gRr7/0oUYAeJJwCRmd5a3OeGahRZtSptfn4dBcLcLP9a3jj9ZEIgOgUV8zjJobjFCcnKIF QHrecwLdIGrRbo7eMfe8Zip1w7UOs8I= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1778284426; a=rsa-sha256; cv=none; b=O7Q9ZU8y05CD5QjpRd/0+wfgQ6cPNzjOcmW7+PDeHzYgLOH046l6LXpIkbd8Yuk5zrES+Y 1dDDSIv92dGXxjWNrpAz86TeVgVPkKFQZFTn1P8hKiQRZbJbMqzX9EiZEWYHS4/7pnpAN5 pJmVJcylGDoo68iVWMXkFKAh0+tqtxU= ARC-Authentication-Results: i=1; imf15.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=korg header.b=FyXfE1Bw; dmarc=none; spf=pass (imf15.hostedemail.com: domain of akpm@linux-foundation.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id 2D4296024D; Fri, 8 May 2026 23:53:46 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8A107C2BCB0; Fri, 8 May 2026 23:53:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1778284425; bh=VWosNBs3YnxgmEDyU8/Ih9kX3QO9bATo1LcNhVdrsvc=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=FyXfE1Bw17tGd84Y1nB23Z4B842vomjgd0qwV5ygZ3GLhlA47c6eItIXl4WWJDTdN s+U4YbcPMwY4QUDuBJwcHVVV8x89mBrzJTtzzv+f2R/Fo1rc4wnG3wUFzhx7NZlrGC pB6Vh+khkAmXJXplPLimbtqRIox/coQg0jO2CrRg= Date: Fri, 8 May 2026 16:53:45 -0700 From: Andrew Morton To: Frederick Mayle Cc: android-mm@google.com, kernel-team@android.com, Kalesh Singh , Suren Baghdasaryan , "Matthew Wilcox (Oracle)" , Jan Kara , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/readahead: no PG_readahead on EOF Message-Id: <20260508165345.b40a73da1dbb45a95c55c0c1@linux-foundation.org> In-Reply-To: <20260508181237.670645-1-fmayle@google.com> References: <20260508181237.670645-1-fmayle@google.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: A2169A0002 X-Stat-Signature: chtsk38o4cequmnntimnsh94tmiizjtk X-Rspam-User: X-HE-Tag: 1778284426-215201 X-HE-Meta: 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 rj16DWkl sMzzwRUvXRvUTWa2CjV9ARnkD4NVf6s8ulFd+7QFE7JYITzwp/8PoFSAQDEbGsGRV1VWydnL7Yz1G+WO5wZt0Xfuaqg+VIHQGJ35FfeI04NPWgwMnJMI2XhFCTj420VUaYZebNJmfF3kXkoLVf/1ikCHZK140Zzfwv23j2n0kmXAdDfwDgMk9pv6jVEuiFLS5FQ3eMaVM+/C7A5M6O3E3qMqxr6tGdYskHPiaXMplHRX38YB5zmJ1VnAPpljlfN6twnbS8Gq93fTKwlAQF7PPjEtjXycl3iWqR+GuhTZBM7ZpEqhq5e848PDzheflu5L3bnzoC2xOyHO4NfzwoHOh6S7X5A8diGazpA63uLsC+J9USCZyyVu6/Cay6IbhMR6BiSvsmmaGNkq43Ot3Db4GFn1M/mWLhJf5qWClYEHfT49OjAUtzOhZz+eooQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, 8 May 2026 11:12:31 -0700 Frederick Mayle wrote: > When readahead pulls in all the remaining pages for a file, setting the > readahead bit is counter productive. The async readahead it would > trigger would almost certainly be a no-op. Additionally, for mmap'd file > IO, the readahead bit limits the fault around [0], There is no "[0]". > causing an extra > minor fault when the page is accessed. > > This was discovered when looking at /sys/kernel/tracing/events/readahead > traces for a simple program. With the patch applied, fewer > page_cache_ra_unbounded calls are observed. > > [1] do_fault_around calls filemap_map_pages, which finds eligible pages > by calling next_uptodate_folio [2]. next_uptodate_folio skips pages > with PG_readahead set [3]. > > Link: https://github.com/torvalds/linux/blob/v7.0/mm/filemap.c#L3921-L3939 [2] > Link: https://github.com/torvalds/linux/blob/v7.0/mm/filemap.c#L3721-L3722 [3] > Cc: Kalesh Singh > Cc: Suren Baghdasaryan > Signed-off-by: Frederick Mayle AI review found a little race: https://sashiko.dev/#/patchset/20260508181237.670645-1-fmayle@google.com