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imf07.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=L0ekHcU8; spf=pass (imf07.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=1774990252; a=rsa-sha256; cv=none; b=rKlVMQX++UrrpDzB6qQT9iVo57bwIN3JkLsl0rAylgQhcHAYyAgub8F+aXWUy6rzvEovbX e+gCZH92EqopyUYCOWflwmet8IG0VQcKekU3pTgSulfs3Woc92czY8ArnlqtLqTpI6jhR5 xDTY9m850jKOyb9lKgAbUGIrQCvfV+I= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id E29E043E75; Tue, 31 Mar 2026 20:50:50 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 120B0C19423; Tue, 31 Mar 2026 20:50:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1774990250; bh=VK5A4yy0VGMGiyXdNogpkOycz3ulih/Q35ZzZi3/ebQ=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=L0ekHcU8aNxw4cMIJhgWfXXXKP5fXHi3LkO2rqW6zLNI1wPu7ssDqAQmTPZz580wD nwl6fHS2MgUzWVlrLtfcWMKq2s/RGhvBBceLAwg30j6zxYztucryxJC+X9diEyRi9z GtxdAg+bnItIiYefGAHCHK+6PjEYfhGFVwTeVGbGwjK8R50ZStqSIqwCDr748/goSN hzZq1G9UCmZu82yR/jX9kOb/TqZC1ZYVpvr7naTxHK+jaNiqZv6UINRR7LTKblzygU pVPzl5c7sW4GqgitT4Dr0PMTWnAyW5wxlbyy+mFx6HMEQlKO9b1wOXSSzQ9QZMWSNc 9wcO0z/+FPeDw== Message-ID: <37132e09-9c03-4afc-bc73-4bca416c5343@kernel.org> Date: Tue, 31 Mar 2026 22:50:32 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH mm-unstable v4 5/5] mm/khugepaged: unify khugepaged and madv_collapse with collapse_single_pmd() To: "Lorenzo Stoakes (Oracle)" Cc: Nico Pache , linux-kernel@vger.kernel.org, linux-mm@kvack.org, 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, jackmanb@google.com, jack@suse.cz, jannh@google.com, jglisse@google.com, joshua.hahnjy@gmail.com, kas@kernel.org, lance.yang@linux.dev, Liam.Howlett@oracle.com, lorenzo.stoakes@oracle.com, 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: <20260325114022.444081-1-npache@redhat.com> <20260325114022.444081-6-npache@redhat.com> <7760c811-e100-4d40-9217-0813c28314be@lucifer.local> <0223d45b-e8b4-49a7-882b-477250d0c14d@kernel.org> <26fcec86-ee78-4f5c-8ca5-0e6230699cfd@kernel.org> <440d6b8a-d299-43eb-83b5-6625f9468e5e@lucifer.local> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 6525F40009 X-Stat-Signature: 84sqyp31be1jqsx18zd5kphpz86pc6di X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1774990252-469651 X-HE-Meta: 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 3zGkE3yj SkuZlTXCrrZz23sQ6SKW1KIBW7bsLFNwFTzJea6XU5AVlgVlKg9wzsSb6ANYSb5XfELZI4HNMjdJD0SEka2G5mNMsa+t/fOh2nY2phDCUcP05ZfnTw9c7tovNH8L9R5SsFxTySu5ByNKgL7Gy9aZFSuwgM/PBhKClwUvxJDn2bs7LVUeTjBoWNqtDZup1YoCUc2WS3KaEmOlHcMvtsvw++KkIyFSFWj0y6wfMl8VNNRrbNXUwPR8qNAib7Pg2QPcNOJqUGpNI01snYfPGRUAr+3ocZFKYP3MWGJD2+kLjs5L5qIXVOFlJcjoiNPC9U/tDpHUbl6PqiRbr14FiQ7Po7ohkltQVNmmQEbYAvPQrytBn8BC8LTiP3n5iXg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 3/31/26 22:06, Lorenzo Stoakes (Oracle) wrote: > On Tue, Mar 31, 2026 at 10:00:58PM +0200, David Hildenbrand (Arm) wrote: >> On 3/31/26 16:15, Lorenzo Stoakes (Oracle) wrote: >>> >>> That updates mmap_unlocked which will be handled in the loop or on exit: >>> >>> if (mmap_unlocked) { >>> ... >>> mmap_read_lock(mm); >>> mmap_unlocked = false; >>> *lock_dropped = true; >>> ... >>> } >>> >>> result = collapse_single_pmd(addr, vma, &mmap_unlocked, cc); >>> >>> ... >>> >>> out_maybelock: >>> /* Caller expects us to hold mmap_lock on return */ >>> if (mmap_unlocked) { >>> *lock_dropped = true; >>> mmap_read_lock(mm); >>> } >>> >> >> Right. >> >> The original code used >> >> bool mmap_locked = true; >> >> If the fix get squashed, maybe we should revert to that handling to >> minimize the churn? > > Well collapse_single_pmd() and all descendents would need to be updated to > invert the boolean, not sure it's worth it. The code is confusing me. In the old code, collapse_single_pmd() was called with "mmap_locked == true" and set "mmap_locked=false". Now we call it with "mmap_unlocked=false" and it sets "mmap_unlocked=true". So far so good. However, collapse_scan_pmd() consumed "mmap_locked", now it effectively consumes "mmap_unlocked". I think I have to squash your fix into Nicos patch to make sense of this. :) -- Cheers, David