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b=Zw3zRPkO1axEGr8w1PtyxGjhG34U26F9uvpVsF/iQuxX5UZ7OfEahljVnMaYzKpcUp2YobffEfbLUB2gO5d1abRfkJHx4LgO1WgNWvDtisz4n+dCdrxcF0hL2DPSwLrg7cdNgz3PI6Hgqaq8tKAe0tvHtpUOd9ugDC6jbJDBlww= Received: from 30.74.144.113(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0WnERfV8_1756966283 cluster:ay36) by smtp.aliyun-inc.com; Thu, 04 Sep 2025 14:11:24 +0800 Message-ID: <8cf7a0c6-be15-4935-827b-a6000395d545@linux.alibaba.com> Date: Thu, 4 Sep 2025 14:11:23 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] mm: Enable khugepaged to operate on non-writable VMAs To: Dev Jain , akpm@linux-foundation.org, david@redhat.com, kas@kernel.org, willy@infradead.org, hughd@google.com Cc: ziy@nvidia.com, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, baohua@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20250903054635.19949-1-dev.jain@arm.com> From: Baolin Wang In-Reply-To: <20250903054635.19949-1-dev.jain@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 1619D40014 X-Stat-Signature: ag5c1zmd5miw9pypozkmg6ctdxqsqgai X-Rspam-User: X-HE-Tag: 1756966288-270230 X-HE-Meta: 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 aNYTMx6O 4N3zLO2S4HeiVJTmgJ0opqKFnQ3VCgiWOMMIT2lnC0FZXGGj2clcNCf2v8f9g3yzpBvg+YFCu7/c71nxdk92UijjnhEHmwq/ape55vwomAj5yFYmBhPt9E4hj/lF2/1jiOVkHiVATMgmnfAyCF+zYPzgcWKPPPBKXkzOFw2huEJQ++7bzEl6igxy3DzFaeB1VMyGEDCVwbqNc1iNbrDrt5dB0/HrbOlzF+ra3emfWT9fv267vKVJW2Pb8wz2w1/ZCilxwbI4g0SHYVHufVClCawqDrSoByJ9qQVYiUrom61My00k2RXjtxHPVReBtEzcRoXEBdAACgrYhlxbIk8sV4DW3jZEUsMhwSvwVs+8zkIRSorQ= 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 2025/9/3 13:46, Dev Jain wrote: > Currently khugepaged does not collapse a region which does not have a > single writable page. This is wasteful since non-writable VMAs mapped by > the application won't benefit from THP collapse. Therefore, remove this > restriction and allow khugepaged to collapse a VMA with arbitrary > protections. > > Along with this, currently MADV_COLLAPSE does not perform a collapse on a > non-writable VMA, and this restriction is nowhere to be found on the > manpage - the restriction itself sounds wrong to me since the user knows > the protection of the memory it has mapped, so collapsing read-only > memory via madvise() should be a choice of the user which shouldn't > be overriden by the kernel. > > On an arm64 machine, an average of 5% improvement is seen on some mmtests > benchmarks, particularly hackbench, with a maximum improvement of 12%. I also wondered about the writable check before, but never dug into the history. The result looks nice. > Signed-off-by: Dev Jain > --- LGTM. Reviewed-by: Baolin Wang