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Fri, 26 Dec 2025 00:31:23 -0800 (PST) MIME-Version: 1.0 References: <20251226063759.4020782-2-tongweilin@linux.alibaba.com> <915dc88b-9131-4520-a2f2-facadc887bbd@linux.alibaba.com> In-Reply-To: <915dc88b-9131-4520-a2f2-facadc887bbd@linux.alibaba.com> From: Barry Song <21cnbao@gmail.com> Date: Fri, 26 Dec 2025 21:31:12 +1300 X-Gm-Features: AQt7F2qQ6-b32qG0-PITUSPaNlNbQaGfg_aC_VktZpMRs77vq1i3irw977ou9Bw Message-ID: Subject: Re: [RFC PATCH] arm64: Kconfig: enable ARCH_WANTS_THP_SWAP for all pagesizes To: Weilin Tong Cc: Catalin Marinas , Will Deacon , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Andrew Morton , David Hildenbrand , linux-mm@kvack.org, baolin.wang@linux.alibaba.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: t8nq3e63cw6kzxchdrrruf8qhkxthyob X-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: E224720005 X-HE-Tag: 1766737884-869471 X-HE-Meta: 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 mPpJBo0/ VS3N0K5YdqZ1u8Ea7/0ObOzXEAEEe5DAp77fSwx/mNp9AwGvtCgiSnKZST6oqVHdnJm/Y1OlqjkUn9cXKgwdKK6HBAPve6K0z7MPgu9FVSsC/UWscyLxA4RbOIWAMHep3TDwIDAElFEHvIrVhNARcTl6I71+uqPQryOupNbV6OMcbS++IHudDPKeZ+RXQzkdroSV/4cLupPMrB3rTzJuQUx0GIKlWszjtwE/gT6zVrL06KFfXM/HKAeNVK+H9Te14TEAvz0K63CR5QftUh9kTxLx3dm9LggfQTVhQszLEqjtuybTo+x30j4dcVfzKwHYGEcJQt4us2ScOktsIRbkibYjGzDAI2Q1IyenSmCtuhmfaMjoaQSluZvbUBpeEM2XyGgt8zRUWQEhSeyYyPCiwhScUKmoRJwOrmxCdFrMmle9z5aQ= 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 Fri, Dec 26, 2025 at 9:18=E2=80=AFPM Weilin Tong wrote: > > > =E5=9C=A8 2025/12/26 14:52, Barry Song =E5=86=99=E9=81=93: > > On Fri, Dec 26, 2025 at 7:39=E2=80=AFPM Weilin Tong > wrote: > > Currently, ARCH_WANTS_THP_SWAP was limited to 4K page size ARM64 kernels,= but > large folios requiring swapping also exist in other page size configurati= ons > (e.g. 64K). Without this config, large folios in these kernels cannot be = swapped > out. > > Here we enable ARCH_WANTS_THP_SWAP for all ARM64 page sizes. > > I no longer recall why this was not enabled for sizes other than > 4 KB in commit d0637c505f8a ("arm64: enable THP_SWAP for arm64"), but > it appears to be fine, and the swap cluster size should also be > more friendly to PMD alignment. > > > #ifdef CONFIG_THP_SWAP > #define SWAPFILE_CLUSTER HPAGE_PMD_NR > #define swap_entry_order(order) (order) > #else > #define SWAPFILE_CLUSTER 256 > #define swap_entry_order(order) 0 > #endif > > > Thank you very much for taking the time to review this patch during the h= oliday. Wishing you a happy holiday as well! > > I appreciate you pointing out this optimization. We initially noticed the= issue because, on ARM64 kernels with 64K page size, if large folios are us= ed in shmem, they cannot be swapped out as a whole during shmem_writeout() = due to the config limitation, > and are forced to split instead=E2=80=94which is something we wanted to a= void. > > It seems that this change will help enable better swap operations for lar= ge folios. Thank you again for your feedback! Right, I believe this is the correct direction. Just double-check that the MTE-related functionality works. Take a look at commit f238b8c33c6738 ("arm64: mm: swap: support THP_SWAP on hardware with MTE").