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 0612ECD4F26 for ; Tue, 12 May 2026 07:42:54 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 6ED0D6B0092; Tue, 12 May 2026 03:42:53 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 6C3B76B0093; Tue, 12 May 2026 03:42:53 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 5DB056B0095; Tue, 12 May 2026 03:42:53 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id 513946B0092 for ; Tue, 12 May 2026 03:42:53 -0400 (EDT) Received: from smtpin04.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay02.hostedemail.com (Postfix) with ESMTP id F18F71203EB for ; Tue, 12 May 2026 07:42:52 +0000 (UTC) X-FDA: 84757976184.04.07A272A Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf18.hostedemail.com (Postfix) with ESMTP id E1AA21C0007 for ; Tue, 12 May 2026 07:42:50 +0000 (UTC) Authentication-Results: imf18.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b="AXMgw/kW"; spf=pass (imf18.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=1778571771; 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=9X6Ff3yD8depbZIBO8iQRidsRYXduQ3SBDQPy2RgJls=; b=2lBVihR/n70c6+Jg3v9qy7bkr6fxySS7VX/bHZik3uJxqnUTpqtnBFBBocY09Bjc8sWs7I KPVdniIeGtFitgfElZlCmiDeySo2i/Coh/gIW6GimBe1r2x4VcdsX3Ok7bGLJNw3rW+NR8 o7GMo5HDMWLx6KiHOlxPz7wZOsDEAAI= ARC-Authentication-Results: i=1; imf18.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b="AXMgw/kW"; spf=pass (imf18.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; s=arc-20220608; d=hostedemail.com; t=1778571771; a=rsa-sha256; cv=none; b=mm3thM60HcfvEJzVSdYvLmWbf0EVGQtZ7Q/JScyMYSiutO4iJZVaPhKLbUUvCyOrXWJk0Y TXWC5EpoKw80niywjqIc2Dck9oPN6WJJluY4sl280lyezxpd42YfXd7hbC31LRnO6V4qDL JejUo0ZvaEciVgh2P5pNZoP+1xP0V9Y= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id D61C144274; Tue, 12 May 2026 07:42:49 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 567D9C2BCB0; Tue, 12 May 2026 07:42:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1778571769; bh=iB8tMCv0MnNsT4JdZSVwpaqxrQgKB7oJIZ1Ch8nbSQE=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=AXMgw/kWeXATu0nbAK7QZZ8AuBWGNIn0QfGbj0HLOhiUj+fUEZM6qPW+6j0WW+Rh3 mJOswvrr21Mk22eRCPWcEmuOtDN9w7/rWEX/cgJ2Z22jGV0Mq3CQNLzjGfzJ5qhqOl Jd+8UCodmDz5uxv/1M9vXs1W4CTu8q0Y2TvZqEEiTAbm3U6DvYhb4S8mdMI03+GSpx HxSvUoofnBHiZHIfwcgWvMqCA+LC3fRWXTQkPV4J1MyCai8N2ds+e+glhrAQp/N2L+ 2PM5LXPQbTEAPg+cQhNe2zVGPj6lMPMkLuEYE8pf3IewN5wc0p3ruMZHCvXJmDZq/c tYsmkI+ofRRMg== Message-ID: Date: Tue, 12 May 2026 09:42:37 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH mm-unstable v17 05/14] mm/khugepaged: require collapse_huge_page to enter/exit with the lock dropped To: Nico Pache , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org Cc: aarcange@redhat.com, akpm@linux-foundation.org, anshuman.khandual@arm.com, apopple@nvidia.com, baohua@kernel.org, baolin.wang@linux.alibaba.com, byungchul@sk.com, catalin.marinas@arm.com, cl@gentwo.org, corbet@lwn.net, dave.hansen@linux.intel.com, dev.jain@arm.com, gourry@gourry.net, hannes@cmpxchg.org, hughd@google.com, jack@suse.cz, jackmanb@google.com, jannh@google.com, jglisse@google.com, joshua.hahnjy@gmail.com, kas@kernel.org, lance.yang@linux.dev, liam@infradead.org, ljs@kernel.org, mathieu.desnoyers@efficios.com, matthew.brost@intel.com, mhiramat@kernel.org, mhocko@suse.com, peterx@redhat.com, pfalcato@suse.de, rakie.kim@sk.com, raquini@redhat.com, rdunlap@infradead.org, richard.weiyang@gmail.com, rientjes@google.com, rostedt@goodmis.org, rppt@kernel.org, ryan.roberts@arm.com, shivankg@amd.com, sunnanyong@huawei.com, surenb@google.com, thomas.hellstrom@linux.intel.com, tiwai@suse.de, usamaarif642@gmail.com, vbabka@suse.cz, vishal.moola@gmail.com, wangkefeng.wang@huawei.com, will@kernel.org, willy@infradead.org, yang@os.amperecomputing.com, ying.huang@linux.alibaba.com, ziy@nvidia.com, zokeefe@google.com References: <20260511185817.686831-1-npache@redhat.com> <20260511185817.686831-6-npache@redhat.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: <20260511185817.686831-6-npache@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Queue-Id: E1AA21C0007 X-Rspamd-Server: rspam06 X-Stat-Signature: urtgg3fh1zh46kw9ro6pw7k5fmr8dj9p X-HE-Tag: 1778571770-677215 X-HE-Meta: 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 OrZGfYez UinyK9eF6yYVxFwEKtaCV0PmL/OxRZeGBriLpPmEFO5v0HicOSd0Xqc9jW36zS/Hk235CRHNBKZCmQ8VtHagC7P+pUty+YoNA+TBkgrXZ0HS2Vqd7WEOTWMaToSxYas1R3WMpZnZL72SOO+0+wJ4hLMj6nV+Uyc+CBA0fSArS2rXNPNF9pe8NCtE2wGtg8JVTgKVpIk05EXHzJwzuP6xbDoEAgZ7QHqSgEuHCSX6Ga+iIX1zRqyAZB47mi3Vuux1zvWchm8hbe+0E767HV4uFjoPHXkRCPFUkjKjscEdN4xMjO3SErKnC/9H6hkLwJgKN/k3izAyKjQ7HGn2wyHD0VyFmQlCuqMSI1yBxjVJ/DUQwP7yxYWhRHqoqQ3ZsyODbwSRYmBZbh+bptiVOe5qO8JWy+jpX/qq6eYI3IdE34gZ/SgM= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 5/11/26 20:58, Nico Pache wrote: > Currently the collapse_huge_page function requires the mmap_read_lock to > enter with it held, and exit with it dropped. This function moves the > unlock into its parent caller, and changes this semantic to requiring it > to enter/exit with it always unlocked. > > In future patches, we need this expectation, as for in mTHP collapse, we > may have already have dropped the lock, and do not want to conditionally > check for this by passing through the lock_dropped variable. > > No functional change is expected as one of the first things the > collapse_huge_page function does is drop this lock before allocating the > hugepage. > > Signed-off-by: Nico Pache > --- > mm/khugepaged.c | 18 ++++++++++-------- > 1 file changed, 10 insertions(+), 8 deletions(-) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index 27465161fa6d..37a5f6791816 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -1199,6 +1199,14 @@ static enum scan_result alloc_charge_folio(struct folio **foliop, struct mm_stru > return SCAN_SUCCEED; > } > > +/* > + * collapse_huge_page expects the mmap_read_lock to be dropped before > + * entering this function. "before entering." Talking about "this function" after naming it sounds odd. Also, there is only an "mmap_lock". > The function will also always return with the lock > + * dropped. "collapse_huge_page expects the mmap_lock to be unlocked before entering and will always return with the lock unlocked." Or something simple like that? > The function starts by allocation a folio, which can potentially > + * take a long time if it involves sync compaction, and we do not need to hold > + * the mmap_lock during that. We must recheck the vma after taking it again in > + * write mode. > + */ "... to avoid holding the mmap_lock while allocating a THP, as that could trigger direct reclaim/compaction. Note that the VMA must be rechecked after grabbing the mmap_lock again." ? Ending up with something like "collapse_huge_page expects the mmap_lock to be unlocked before entering and will always return with the lock unlocked, to avoid holding the mmap_lock while allocating a THP, as that could trigger direct reclaim/compaction. Note that the VMA must be rechecked after grabbing the mmap_lock again." > static enum scan_result collapse_huge_page(struct mm_struct *mm, unsigned long address, > int referenced, int unmapped, struct collapse_control *cc) > { > @@ -1214,14 +1222,6 @@ static enum scan_result collapse_huge_page(struct mm_struct *mm, unsigned long a > > VM_BUG_ON(address & ~HPAGE_PMD_MASK); > > - /* > - * Before allocating the hugepage, release the mmap_lock read lock. > - * The allocation can take potentially a long time if it involves > - * sync compaction, and we do not need to hold the mmap_lock during > - * that. We will recheck the vma after taking it again in write mode. > - */ > - mmap_read_unlock(mm); > - > result = alloc_charge_folio(&folio, mm, cc, HPAGE_PMD_ORDER); > if (result != SCAN_SUCCEED) > goto out_nolock; > @@ -1526,6 +1526,8 @@ static enum scan_result collapse_scan_pmd(struct mm_struct *mm, > out_unmap: > pte_unmap_unlock(pte, ptl); > if (result == SCAN_SUCCEED) { > + /* collapse_huge_page expects the lock to be dropped before calling */ > + mmap_read_unlock(mm); > result = collapse_huge_page(mm, start_addr, referenced, > unmapped, cc); > /* collapse_huge_page will return with the mmap_lock released */ Acked-by: David Hildenbrand (Arm) -- Cheers, David