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 4382EC9830C for ; Wed, 23 Sep 2026 12:24:17 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 620126B0095; Wed, 23 Sep 2026 08:24:16 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 5F83D6B0096; Wed, 23 Sep 2026 08:24:16 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 50EB66B0098; Wed, 23 Sep 2026 08:24:16 -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 30DDD6B0095 for ; Wed, 23 Sep 2026 08:24:16 -0400 (EDT) Received: from smtpin14.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay09.hostedemail.com (Postfix) with ESMTP id B5D7C80798 for ; Wed, 23 Sep 2026 12:24:15 +0000 (UTC) X-FDA: 85244944470.14.917C7BC Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf17.hostedemail.com (Postfix) with ESMTP id D6DBB40003 for ; Wed, 23 Sep 2026 12:24:13 +0000 (UTC) Authentication-Results: imf17.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=HcO6poHv; spf=pass (imf17.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=1790166254; 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=Fz7wnacojcCCtGK9ldyNPikquj5YfjQzpeki9G2X8DI=; b=wFn73TB4mbYcs7EWYg/8AGMhtQrijScYT262S6PgnR0ecOwihbjn8IklfZFN7f7tps3+lN m0/a053OoDMwBlzZ9wvJE74/8F1kBN27E9a/SE7CErpzdEN5rp3FHDprSLscb1cN+uHEvg lzmVE4OdapxS6jcukVfIo8DSRnGNjU8= ARC-Authentication-Results: i=1; imf17.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=HcO6poHv; spf=pass (imf17.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-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1790166254; b=dEdRBBlciB/qSyafo+PelSV+pzucJdGmUc7BaxYwcj7i7GS6DqZC5zsa/FHRFnS7R6cSZw 34/+dyPHNrVsWAU2InPfSbHgaaFJByzhDESzaXQ/Ma76uyOIF2VyMnhU3dNxbIB/b1RQYk ptUSoQslNPt4hPoefdNkbMtCGLDc7us= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 06907400AE; Wed, 23 Sep 2026 12:24:13 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 823F01F00893; Wed, 23 Sep 2026 12:24:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790166252; bh=Fz7wnacojcCCtGK9ldyNPikquj5YfjQzpeki9G2X8DI=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=HcO6poHvX+9qlNd1qxKmYnGXiuf9GFggnkCljgozbVFRxRyTBLJG0U7eTh5rZxKze aVNJliJp+v7IBHUnr9hS+uzT7jnxsG7FVQcxPdoqH/67j71dEZK5oNsFx5k7U7secu k+2nWm9wFzKZyzJHySiZXiEUpKcbB+Dy4YVtvbJVoQQUmUDrhtZsHng+pTepwEkdRR m2q4EKP3fXaHsYZ1I+wKuAwAzAPLk9En8BV+BJ2JwEeUPrcqn6YLB/ea6e2sE0cif6 a0QPuavKg4YY6UuunaYulXXyaKh6k23jJMSaiR6UGtOXbNKdKIz8dRPuEbUgmwArME Gasc4NMMkitrQ== Message-ID: <2add40dc-6541-41e3-8233-521cce7e0d33@kernel.org> Date: Wed, 23 Sep 2026 14:24:04 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 05/12] 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: <20260916093145.4022188-1-kirill@shutemov.name> <20260916093145.4022188-6-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: <20260916093145.4022188-6-kirill@shutemov.name> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: D6DBB40003 X-Stat-Signature: k51pmoua5ssqpwp4swp1roqo8yjnfauf X-Rspam-User: X-HE-Tag: 1790166253-198127 X-HE-Meta: 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 dH7AwACQ HTwMJ74MuRfNsIKunyjdKVKzgUuDGTQnHBml/Kys6yYfA2Mpq8SG0neBVyiqhvgGLfhFQuSq+7vqRDO9rZC4ofpKA5Xor8GWiCiroXxqWN053iDv3UQs0z/a8nadrEknpA82wkInmtwqFFbSZCfBWw0KOzM/G4NwXGqkDYHhvKIquq/ZgwU6Tmuce+aB70jJzDKjYy0TCv3Jo4f21rAuT3ZtDL2yFcb+ArikXQ5UQGddvH9xUU6EXYN3Z5RP7N4QK/Iy0ZPNVCJ4tdTJwIVFt1M402l12Sewsv0j1vzrfGeE/LL9/RRD+KYAWrEId49ODac3DtMKN+d4gZyk= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/16/26 11:31, 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. Agreed. Removing plenty of these is_khugepaged checks is nice. > > 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. > > 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. Fair. > > 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. Worth putting this into a separate patch? Likely not. > > Assisted-by: LLM > Reviewed-by: Zi Yan > Reviewed-by: Baolin Wang > Signed-off-by: Kiryl Shutsemau (Meta) > --- > mm/collapse.h | 31 ++++++++++++- > mm/khugepaged.c | 114 ++++++++++++++++++++++++++---------------------- > 2 files changed, 93 insertions(+), 52 deletions(-) > > diff --git a/mm/collapse.h b/mm/collapse.h > index b115034d9018..7044dc71c7c2 100644 > --- a/mm/collapse.h > +++ b/mm/collapse.h > @@ -45,8 +45,37 @@ enum scan_result { > SCAN_PAGE_DIRTY_OR_WRITEBACK, > }; > > +/* What a collapse is allowed to do, decided by the caller that asks for it */ > +struct collapse_policy { > + /* Limits, stated per PMD; HPAGE_PMD_NR means "no limit" */ > + unsigned int max_ptes_none; > + unsigned int max_ptes_swap; > + unsigned int max_ptes_shared; > + > + /* Take no swapped-out or shared PTE into a sub-PMD collapse */ > + bool strict_sub_pmd; Reading this variable name without the documentation I have no idea what it means. It looks like the wrong abstraction. Maybe you instead want to split max_ptes_swap and shared to a PMD and non-PMD case? I am also confused why you use "strict_sub_pmd" in the collapse_max_ptes_none() handler below? Something seems odd, as it doesn't amtch the description here. > + > + /* Leave clean lazyfree folios to reclaim rather than collapse them */ > + bool skip_lazyfree; > + > + /* Refuse a range with no sign of use */ > + bool require_referenced; > + > + /* Map the PMD over a file collapse instead of leaving it to a fault */ > + bool install_pmd; Confusing. If some of these policies are anon-/ file-specific, the name should indicate that, so there is less head scratching. > + > + /* Write dirty pages back and retry once instead of refusing them */ > + bool writeback_dirty; > + > + /* How hard to try for a destination folio */ > + gfp_t gfp; > + > + /* Which VMAs are eligible, as thp_vma_allowable_orders() spells it */ > + enum tva_type tva_type; > +}; > + > struct collapse_control { > - bool is_khugepaged; > + struct collapse_policy policy; > > /* Num pages scanned per node */ > u32 node_load[MAX_NUMNODES]; > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index 8889f75cf45f..cb08789b2d38 100644 > --- a/mm/khugepaged.c [...] > > +/* khugepaged collapses on its own initiative, so it obeys its own settings */ > +static void collapse_policy_khugepaged(struct collapse_policy *p) > +{ > + p->max_ptes_none = READ_ONCE(khugepaged_max_ptes_none); > + p->max_ptes_swap = READ_ONCE(khugepaged_max_ptes_swap); > + p->max_ptes_shared = READ_ONCE(khugepaged_max_ptes_shared); > + p->strict_sub_pmd = true; > + p->skip_lazyfree = true; > + p->require_referenced = true; > + p->install_pmd = false; > + p->writeback_dirty = false; > + p->gfp = alloc_hugepage_khugepaged_gfpmask(); > + p->tva_type = TVA_KHUGEPAGED; > +} > + > +/* MADV_COLLAPSE was asked for explicitly, so it is not held to those */ > +static void collapse_policy_forced(struct collapse_policy *p) Why are we not calling this collapse_policy_madvise to match its description here? [...] > @@ -2943,6 +2952,9 @@ static void khugepaged_do_scan(struct collapse_control *cc) > > lru_add_drain_all(); > > + /* One policy for the whole pass, so every table is treated the same */ just drop that comment. -- Cheers, David