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 51138CA5FA3 for ; Mon, 28 Sep 2026 19:26:14 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 7B6B86B00A0; Mon, 28 Sep 2026 15:26:13 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 767946B00A1; Mon, 28 Sep 2026 15:26:13 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 656A66B00A2; Mon, 28 Sep 2026 15:26:13 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id 3EBAE6B00A0 for ; Mon, 28 Sep 2026 15:26:13 -0400 (EDT) Received: from smtpin15.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay03.hostedemail.com (Postfix) with ESMTP id C7D4DA02F0 for ; Mon, 28 Sep 2026 19:26:11 +0000 (UTC) X-FDA: 85264151742.15.ABD1364 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf25.hostedemail.com (Postfix) with ESMTP id E98EBA0004 for ; Mon, 28 Sep 2026 19:26:09 +0000 (UTC) Authentication-Results: imf25.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=Wcp7cHX6; spf=pass (imf25.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@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=1790623570; 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=0Y8OPyB+lH5YUHprZNR3SaW3cfSHre/dvyOuPKtpY6o=; b=qdhsMpm0Nbawz308RrlxvQJGXdScjOxr+OBTcTcsG9JZnvJOXewoyb6qkNxda4Tk0VBZll o85DJ0LVJ1PRQtnyJLjSsgR0/uPjcyouvUFxRaEIZq3FuhRyR4tSU5pM9nWUNCts8ZeY+Q 86D+FDmEjtnUVmH95RlOFwljmxG/Y4A= ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1790623570; b=EaKY0e7SZvarONnNM7v1/C5BUSK9FeVEifjQmppSBWmuZWxxPAgjxO2ytCvJqzul3GNG1L 6ADFohiSppaCFfVJU2c6FtfjJJc9r9+cJuyJXaU9bZcy4qTGzXvL+BE8SH44cB5eB4ENET tOHzW5eWIuMPyqPGvH+npJ8L0BRYZCY= ARC-Authentication-Results: i=1; imf25.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=Wcp7cHX6; spf=pass (imf25.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id C7E1C41831; Mon, 28 Sep 2026 19:26:08 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0613A1F000FF; Mon, 28 Sep 2026 19:26:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790623568; bh=0Y8OPyB+lH5YUHprZNR3SaW3cfSHre/dvyOuPKtpY6o=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=Wcp7cHX6LWHGsQaR9T/tCd3pP+3Nwpky2kHzT10MTDkKhmA8MW27LMPfnHJWAK8YC +vXO4EQfwcr3lSIQ1GPZZy2+hy6VH23tqE8KfCjhgZAJ0QKIAdiG5J+t4BFI0+uLg9 KO7aGLZ8hdbZ+QSsWx3hYZrL8/r5YM6CN+AB2mwngYdlvTUXfd15BksKOrruq9yvvZ TIefRcYgE8qu3JEYFQgUw57Mn63WPUXYwIrFppx3c6UIyOl7JZWzlGzLWob3PCk/+O EPLWWcNcONNuYqNUSC7tCX5D4iB/ual9oq/UXdC2DfBrj+FyQTBM1hX24JImxBGYY6 wVpQ6xWYlCFPA== Message-ID: <335f5274-7174-4fe7-8d29-37a1ed26147b@kernel.org> Date: Mon, 28 Sep 2026 21:26:01 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 05/13] mm/collapse: state what a collapse may do in the policy To: Kiryl Shutsemau , Andrew Morton , Lorenzo Stoakes , Zi Yan , Baolin Wang Cc: "Kiryl Shutsemau (Meta)" , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Vlastimil Babka , Jann Horn References: <20260928100630.21870-1-kirill@shutemov.name> <20260928100630.21870-6-kirill@shutemov.name> 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: <20260928100630.21870-6-kirill@shutemov.name> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: E98EBA0004 X-Stat-Signature: y5d8pxs6mtfixt7i454rfzea8e68hgy6 X-Rspam-User: X-HE-Tag: 1790623569-870604 X-HE-Meta: U2FsdGVkX1+PT+elfjG4IGdQQgtvokdfQEvqvk5SsvD3Q02/7kR5FiJ6tZ+cmaAK+mSiSj/E/lB1lsK1YHtGxlUrPi7fZZd/4I2JnatmqN7GWhDYnbnCWYmmUWqYVgBBrUVj1lj47fFCrySDp05KN0ymfuiGf25MH0j754b6C+Flbmz8FHnJ8E1ZB5h5VeUzRhs7BrxjHLF3XJ7Y9cv4kLxAovkTja52K37HjTyN52NcOpK6smOXAOWUBiewsK1AaBhBqyDINZKdL2a/GG9mk2HZLMHGWgoUiAJzjXHvrHSqpGrruCYL39LsRHCREupYKPTuaoU1NTfIET3ETB9qNH20jlEcVBLfE18iDEEm3g40DhpG7P/zS/cn+qRkOXqFCeu3j4QOLBBsoLDDhvkVl9BlaGHtoQFk7E0vfjRTosvf7N+ApHMY2fD3BgvWQttBSpi2BXRtyA0NIhAHX96MYdSn4Fqbk5ZlxeisvsS15UlxGn/Qyv/BLFE4L55U5lakoyCgvgHYzxlr/HIkIqETqmZbcO9s68j8Muri0+ctF7t1uR3/pyxldcR7pnR1EzR0H6IjuCTMDp4ywueThjFYzWcCrQ7E1p2RofX3yADIuFRI6oR6D84H6yvSTpQzLvAaTg650AamLJU3VLFjFAm/PnyViFMHiqlpENxduoFsc18e+pcK68sFYoJ0rAiM5jcq6sHs3swac1fmdzGIALcq9J3vWzG+AgtEvqJajj+3F/Z2iJJkHZND2FT4ShnHsR348hH2yljRXIrBTq/4OXugYXETcExoFLJIItY1zzBeXSAhQO/+O2xmOVG9yivt9mC8WiiMrt3IkOc9hJVYP5laWzV2nt2Q8rbWtwymOQL8lZanuIOrOgzJi3vevXrwkVvr8p+00c1i8NK5yBp/47Fo1RFMZmibJZ3JWrt8swZsVJ0DVS0/LCWvpj4x6KEy9QftEHJLIDrPFpTzIpQQoI6 qLMwjSBH BCcHgqJQ9MMI7i6E95m8wjNxhrYuIarmsZ+SC0MXLbzcSzfjD5zbPwRUCHuFPcnfwmRbNvDFMolCFdo9EPfHb3GkGxQdeGmHduS8EM8XVhcb05j7eb2hdoceoie2q9S6Sd3vg/ggk/DThGU5f8gKNOQmYkSbrhzezKUWKEU0ckGPYhH1VflzB347TKPy/pxEFAmFfMdnc4WaOodvhR+HkxvXDVVq/bDlAdjwtKZBeng1yvJMx8RIdjY0WDLT3DutlfaOIw4ZZHfdHDZJbzUyUET6cS8vwyMxaoRyB Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/28/26 12:06, Kiryl Shutsemau wrote: > From: "Kiryl Shutsemau (Meta)" > > Tests scattered through the collapse path decide what a collapse is > allowed to do by asking whether khugepaged started it. Between them they > settle: > > - which VMAs are eligible, and how hard to try for a folio; > - how many empty, swapped-out or shared PTEs a window may contain, and > whether a sub-PMD window is held to a stricter rule than a PMD; > - whether a range has to look used, and whether a MADV_FREE'd page is > left alone; > - whether the PMD is mapped as part of the request, and whether dirty > pages are worth writing back and retrying. > > None of those is a fact about khugepaged. Each is something the caller > decided before asking, and the collapse code should not have to look up > who called to find out. > > Add struct collapse_policy for the caller to fill: khugepaged from its > own settings, MADV_COLLAPSE from the fact that a user asked explicitly. > Every test becomes a read of a field, and cc->is_khugepaged goes, having > no reader left. > > The PTE limits come as two sets, one for a PMD-sized window and one for > anything smaller, so that the helpers pick a set for the order and read > it. khugepaged takes no swapped-out or shared PTE into a sub-PMD window, > and empty PTEs only when the knob says all or nothing; the warning for a > knob value in between moves to where khugepaged fills its policy. The > fields only one side reads say which: anon_ or file_. David Hildenbrand > asked for both. > > khugepaged fills the policy once per scan pass, MADV_COLLAPSE once per > call. That is the one change in behaviour. The max_ptes_* limits and the > defrag setting behind the allocation mask are sampled once per pass rather > than on every table. A table scanned early in a pass and one scanned late > are then treated alike. > > collapse_file() also drops a NULL check on the collapse_control. It has > one call site, reached only from collapse_single_pmd(), which dereferences > cc unconditionally, so the check was already dead. > > Assisted-by: LLM > Signed-off-by: Kiryl Shutsemau (Meta) > --- > mm/collapse.h | 41 +++++++++++++- > mm/khugepaged.c | 147 +++++++++++++++++++++++++----------------------- > 2 files changed, 118 insertions(+), 70 deletions(-) > > diff --git a/mm/collapse.h b/mm/collapse.h > index b115034d9018..dcd117071955 100644 > --- a/mm/collapse.h > +++ b/mm/collapse.h > @@ -45,8 +45,47 @@ enum scan_result { > SCAN_PAGE_DIRTY_OR_WRITEBACK, > }; > > +/* How many PTEs of a window may be missing, swapped out or shared */ > +struct collapse_limits { > + /* Counted over a PMD-sized window; HPAGE_PMD_NR means "no limit" */ > + unsigned int max_ptes_none; > + unsigned int max_ptes_swap; > + unsigned int max_ptes_shared; > +}; > + > +/* What a collapse is allowed to do, decided by the caller that asks for it */ > +struct collapse_policy { > + /* Limits for a PMD-sized window */ > + struct collapse_limits pmd; > + > + /* > + * Limits for a smaller window. Its max_ptes_none is either 0 or > + * COLLAPSE_MAX_PTES_LIMIT, the latter meaning all but one PTE of the > + * window whatever its order; any other value counts as 0. > + */ > + struct collapse_limits sub_pmd; > + Yeah, this is cleaner. Skimmed over the remaining stuff and nothing jumped at me Acked-by: David Hildenbrand (Arm) -- Cheers, David