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Wed, 3 Sep 2025 05:03:57 -0400 (EDT) Date: Wed, 3 Sep 2025 10:03:54 +0100 From: Kiryl Shutsemau To: Dev Jain Cc: akpm@linux-foundation.org, david@redhat.com, willy@infradead.org, hughd@google.com, ziy@nvidia.com, baolin.wang@linux.alibaba.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 Subject: Re: [PATCH 1/2] mm: Enable khugepaged to operate on non-writable VMAs Message-ID: References: <20250903054635.19949-1-dev.jain@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250903054635.19949-1-dev.jain@arm.com> X-Rspamd-Queue-Id: 8BE8140008 X-Rspamd-Server: rspam04 X-Rspam-User: X-Stat-Signature: 8ch4tt37t9maf7yhrbju64xu4kikmruc X-HE-Tag: 1756890240-309781 X-HE-Meta: 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 EkEFdHus SYSACEt3d9W3uNJC4ZtBmoNLCDb1B4vp22wB2S+H8LNyTciLlrzGOCa3kWoeT2LUQL5+HP/oQmXUxfHeD7jVrS6GLqbTcduHu13mKCLu8MIY7htOfcO+dG109eFi1EtjpChl16SkJr7QmQonQbLdPY8/4HlxZW4+FDUQDxAvZTFbCNEZ7a9dILYbc8mOnck7Sb5HgktPkF0GDUAcUBUEKmr2na886TH5bxUg7bLTs2gKbAiII/Quy70U1khTKWDeW1EViO2OyBxHkAC1kW6GnqtQ+XkvoKZpQyOV6wjvEbRZL9u71G8ISgI00CGQI0S5/IWSHdtgc5pv1nCDaEQw2CwUzIe6nRsfUZPn9SJr4LwYQptw= 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 Wed, Sep 03, 2025 at 11:16:34AM +0530, 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%. > > Signed-off-by: Dev Jain Reviewed-by: Kiryl Shutsemau -- Kiryl Shutsemau / Kirill A. Shutemov