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imf25.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=arm.com; spf=pass (imf25.hostedemail.com: domain of dev.jain@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=dev.jain@arm.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1741247074; a=rsa-sha256; cv=none; b=xoJvaAZH3t/5Xf7bDkFqHjD7Ao92xqG8GrRBeYm/iBtaZVRyI6bh8XwAU998iIKcdm1thd IIf5M76CC8sg12IPFA3CaMkOmkbfGpvvG5t9hyDKPKnv4rl+7hOcH5aSVQvAxOzu7dN1C6 YIeJCqMOdfB+xllWDDOvgo6fMdrLxBI= Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 7B8C9FEC; Wed, 5 Mar 2025 23:44:46 -0800 (PST) Received: from [10.162.43.28] (K4MQJ0H1H2.blr.arm.com [10.162.43.28]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 414733F66E; Wed, 5 Mar 2025 23:44:28 -0800 (PST) Message-ID: Date: Thu, 6 Mar 2025 13:14:26 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/vma: Do not register private-anon mappings with khugepaged during mmap To: Andrew Morton Cc: Liam.Howlett@oracle.com, lorenzo.stoakes@oracle.com, vbabka@suse.cz, jannh@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, ryan.roberts@arm.com, anshuman.khandual@arm.com, aneesh.kumar@kernel.org, yang@os.amperecomputing.com, david@redhat.com, willy@infradead.org, hughd@google.com, ziy@nvidia.com References: <20250306063037.16299-1-dev.jain@arm.com> <20250305223856.bc1a0c90339cf0d353e8be34@linux-foundation.org> Content-Language: en-US From: Dev Jain In-Reply-To: <20250305223856.bc1a0c90339cf0d353e8be34@linux-foundation.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: gh71sb7cbmwt1gr8fd8xqji35fkrbfta X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 7F235A0009 X-Rspam-User: X-HE-Tag: 1741247074-497030 X-HE-Meta: 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 lD4zk7Bd Ke0jgno42yHmSY+k8qp1Gk/EStDoFxdkDFOvUdt97yrYJaGGtQ7c/SP+lYZ/CuSO7OPevYeh/eRZ6d06Y3Ug+kkf98jXzzccaOWz/U4IewZp1KnI1cKvYLSYJDHPWWsGxwG8N6/7aDqDoDh6flpJn1MrxanclDVG8/fiKopJLBytmO3jsNcOPMY47hySPkkokve8kGcaypRotSfA= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 06/03/25 12:08 pm, Andrew Morton wrote: > On Thu, 6 Mar 2025 12:00:37 +0530 Dev Jain wrote: > >> We already are registering private-anon VMAs with khugepaged during fault >> time, in do_huge_pmd_anonymous_page(). Commit "register suitable readonly >> file vmas for khugepaged" moved the khugepaged registration logic from >> shmem_mmap to the generic mmap path. Make this logic specific for non-anon >> mappings. > > Please fully describe the userspace-visible effects of this bug. Apologies. The userspace-visible effect should be this: khugepaged will unnecessarily scan mm's which haven't yet faulted in. Note that it won't actually collapse because all PTEs are none. Now that I think about it, the mm is going to have a file VMA anyways during fork+exec, so the mm already gets registered during mmap due to the non-anon case (I *think*), so at least one of either the mmap registration or fault-time registration is redundant. > >> Fixes: 613bec092fe7 ("mm: mmap: register suitable readonly file vmas for khugepaged") >> Signed-off-by: Dev Jain > > Thanks, I'll add cc:stable.