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Thu, 08 Jan 2026 15:11:27 -0800 (PST) MIME-Version: 1.0 References: <20251226063759.4020782-2-tongweilin@linux.alibaba.com> In-Reply-To: From: Barry Song <21cnbao@gmail.com> Date: Fri, 9 Jan 2026 12:11:16 +1300 X-Gm-Features: AQt7F2oHOKrzfSL2LssjsEfQPu4bcd9R3NUhDfSnV_B8eZokCpQo4dn2s21CDqQ Message-ID: Subject: Re: [RFC PATCH] arm64: Kconfig: enable ARCH_WANTS_THP_SWAP for all pagesizes To: Will Deacon Cc: Weilin Tong , Catalin Marinas , 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: hyqy3kexfb5ywman6qeqezm9eekg5y38 X-Rspam-User: X-Rspamd-Queue-Id: B126BC000C X-Rspamd-Server: rspam08 X-HE-Tag: 1767913888-96959 X-HE-Meta: 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 7Ts0FAQM pia4uS8R8a9bOu7VEC85v1yb2DdmAtoGlzeKyMCd68IKyJDL+VOVNFaGkvbNoXPJEl1iNu1t3v5BegVcY51zwCLFw38ii93t78YynCwvQJaPvqNljk2XFZRGWdcjn23n6SuoXHs/a7NaROui5rdtHFHIoliOI4AsPmlWFU9AJOK3fEqkJO46qt4g0vew/gyZRy/p1CBlC9fIbdh34ZFVdEz0ptsQVA9ac/zVDMrLZXGMKXjhuXDgLvR3KBeVan43qG1l4XIxph8euTXo1KwEyg1peZb/T6FEBLsrO0X/JYhJuBAtEy7My/tXtLqbCQp8new7v4z3UWJDXr7hImMjaVlX1ifJYELb7/hjqqgWwyLzg4JVD80aYQKEJh8Xt0dgeohXlFIW1q19pAJI10lDF/x/t6/e+sZrPzQoAP7J7yB2LrBfOAnuS8bCFqeW7BnTNlmvEeUvD0q+Y4/HZModw5stFtV8Qf3nZ9J3u 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, Jan 9, 2026 at 7:29=E2=80=AFAM Will Deacon wrote: > > On Fri, Dec 26, 2025 at 07:52:44PM +1300, Barry Song wrote: > > 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 kern= els, but > > > large folios requiring swapping also exist in other page size configu= rations > > > (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. > > You seemed to be worried about I/O latency in your original post: > > https://lore.kernel.org/all/20220524071403.128644-1-21cnbao@gmail.com/ Will, thanks for pointing this out! With a 16KB page size, a PMD covers 32MB; with 64KB pages, a PMD covers 512MB. So, Weilin, are we ready to wait for 32MB or 512MB to be written out before memory can be reclaimed? By splitting, we can reclaim memory earlier while only part of it has been swapped out. While splitting down to order-0 is not ideal, splitting to a relatively larger order appears to strike a balance between I/O latency and swap performance. Anyway, I don't know :-) Thanks Barry