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 C13D4FF8860 for ; Mon, 27 Apr 2026 12:41:27 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id CFFCF6B0092; Mon, 27 Apr 2026 08:41:26 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id CD75A6B0093; Mon, 27 Apr 2026 08:41:26 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id BED376B0095; Mon, 27 Apr 2026 08:41:26 -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 AE2126B0092 for ; Mon, 27 Apr 2026 08:41:26 -0400 (EDT) Received: from smtpin17.hostedemail.com (lb01b-stub [10.200.18.250]) by unirelay07.hostedemail.com (Postfix) with ESMTP id 51E3C1601C2 for ; Mon, 27 Apr 2026 12:41:26 +0000 (UTC) X-FDA: 84704296572.17.F12E7D2 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf20.hostedemail.com (Postfix) with ESMTP id 7AAA71C0013 for ; Mon, 27 Apr 2026 12:41:24 +0000 (UTC) Authentication-Results: imf20.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=C2h86xCI; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf20.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1777293684; a=rsa-sha256; cv=none; b=bc/fdKIuQwkJpsHqX6PTZ+7qH7jMs0hj4vy4Dl6ms69pEkVl7Zi7AN9ZNNafuPi5lgnQo/ CpJqpBzxdcm1e3XGWGhJ/Ea7KZJKCxPu2oTmlAjdJCqZSHR4KQNCUhsaAnAhuYPzRfBD+9 op2KR60DMeTkcxnYuJL3UlnbCjOWvf0= ARC-Authentication-Results: i=1; imf20.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=C2h86xCI; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf20.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1777293684; 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=0uKPCPXJVBAUSqQlGdOe0MhnLCA3w5VFRWtsUxf7oPw=; b=EsrwFaYrDlDgwLXPppppQNJCV+HkLaje/SZiO+mQxJaYQZumYctBqiIbK2Ihad8fIAqHy8 9EsZF4h+HXg1CQuOslADCDadH9lYFoCqurhpMc8nRfvSeiibd4UBejNBDJ70bK+d5ZNujF u/MKpNYR2PR+e48E/mkIyq64oLrPqDU= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id 87F0E41900; Mon, 27 Apr 2026 12:41:23 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id BC9FFC19425; Mon, 27 Apr 2026 12:41:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1777293683; bh=JSNA+AhXaEfEI0gzCAqHvexyCIAgBK6DaskqKasRfg0=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=C2h86xCI6WB9WS8eJDG7bGUNJHrpHlXBvwrjYQDUuSkI6ngoTSajL+YaByI985DRD 3NaSgOwhJsZQSYo4JrjknnEQCitTSKIcQ67RYTHsxnKnFjoNSjKIFNlt0yZGRjOz4Q 2C+VDm5XRHrAs0k8Z1QN+2Q1Msu8e2V7O0w9ixkIZvlcIJ3071d/um9dhFArk0JZg/ lUeZaFKEfFsChSXeOfwjEGgR31+oFSV1M2/Dcts8tSuTAyH0cx2gjKgCGTT/bL1hun zB1vCEFm0YltGw4bXB7j3gCV+rVIkBLYXjLcEVZZ4WAiltyRwzByYjRA9B1eYt+kGv afdu21bT2PSug== Message-ID: Date: Mon, 27 Apr 2026 14:41:15 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] mm: limit filemap_fault readahead to VMA boundaries To: Frederick Mayle , Jan Kara , Lorenzo Stoakes , Matthew Wilcox , Andrew Morton , Pedro Falcato Cc: Kalesh Singh , Suren Baghdasaryan , android-mm@google.com, kernel-team@android.com, "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Michal Hocko , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260427030148.653228-1-fmayle@google.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <20260427030148.653228-1-fmayle@google.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: 8nq5udniq8xx5kcbrzwcpjuxybmuic1y X-Rspam-User: X-Rspamd-Queue-Id: 7AAA71C0013 X-Rspamd-Server: rspam07 X-HE-Tag: 1777293684-712130 X-HE-Meta: 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 uLUD5dGR U5yK92wHyC4BFy2tZCpKNFg87bKWHummYJ/M5HuCnMvZH8KOrXxIYpXhLjnAv0LsuF0mUsEtRphM1L27ksDGVpBJRcc2cYXVM7WIVDTBPRHLLzNk2aFIZzyMoQdelHjT6ekfQprkdhBPNsQ7OTFtm0QOdhC5J8qjYaGrgywbFN4gP/Ea1wYtuZ/Kks1tX+k8We5awSMdpR8XnDzvm0wyccWPSD5xNoBPDHksxKm0HyZ2F5D3CaWZb+QRj4JyVq/2V+rROWG/aUHGKTV1bF8bhMtmuKIbkfBgGeKfDwKqzZu/ALuREYQ+hKpg8ag== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 4/27/26 05:01, Frederick Mayle wrote: > When a file mapping covers a strict subset of a file, an access to the > mapping can trigger readahead of file pages outside the mapped region. > Readahead is meant to prefetch pages likely to be accessed soon, but > these pages aren't accessible via the same means, so it fair to say we > don't have a good indicator they'll be accessed soon. Take an ELF file > for example: An access to the end of a program's read-only segment isn't > a sign that nearby file contents will be accessed next (they are likely > to be mapped discontiguously, or not at all). The pressure from loading > these pages into the cache can evict more useful pages. > > To improve the behavior, make three changes: > > * Introduce a new readahead_control field, max_index, as a hard limit on > the readahead. The existing file_ra_state->size can't be used as a > limit, it is more of a hint and can be increased by various > heuristics. > * Set readahead_control->max_index to the end of the VMA in all of the > readahead paths that can be triggered from a fault on a file mapping > (both "sync" and "async" readahead). > * Limit the read-around range start to the VMA's start. > > Note that these changes only affect readahead triggered in the context > of a fault, they do not affect readahead triggered by read syscalls. If > a user mixes the two types of accesses, the behavior is expected to be > the following: if a fault causes readahead and places a PG_readahead > marker and then a read(2) syscall hits the PG_readahead marker, the > resulting async readahead *will not* be limited to the VMA end. > Conversely, if a read(2) syscall places a PG_readahead marker and then a > fault hits the marker, the async readahead *will* be limited to the VMA > end. > > There is an edge case that the above motivation glosses over: A single > file mapping might be backed by multiple VMAs. For example, a whole file > could be mapped RW, then part of the mapping made RO using mprotect. > This patch would hurt performance of a sequential faulted read of such a > mapping, the degree depending on how fragmented the VMAs are. A usage > pattern like that is likely rare and already suffering from sub-optimal > performance because, e.g., the fragmented VMAs limit the fault-around, > so each VMA boundary in a sequential faulted read would cause a minor > fault. Still, this patch would make it worse. See a previous discussion > of this topic at [1]. I agree that workloads that do a lot of mprotect() magic likely do not depend on readahead optimizations. But I'm sure we'll learn quickly if that is not the case :) -- Cheers, David