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Wed, 17 Sep 2025 21:51:05 -0700 (PDT) MIME-Version: 1.0 References: <20250916160100.31545-1-ryncsn@gmail.com> <20250916160100.31545-2-ryncsn@gmail.com> In-Reply-To: From: Chris Li Date: Wed, 17 Sep 2025 21:50:53 -0700 X-Gmail-Original-Message-ID: X-Gm-Features: AS18NWBUHzf4JRxxpGz4NBNi-ZdFJXllMYmFHXL-HaEBN1mSBaZpw2RCXXPZ-ak Message-ID: Subject: Re: [PATCH v4 01/15] docs/mm: add document for swap table To: Barry Song <21cnbao@gmail.com> Cc: Kairui Song , linux-mm@kvack.org, Andrew Morton , Matthew Wilcox , Hugh Dickins , Baoquan He , Nhat Pham , Kemeng Shi , Baolin Wang , Ying Huang , Johannes Weiner , David Hildenbrand , Yosry Ahmed , Lorenzo Stoakes , Zi Yan , linux-kernel@vger.kernel.org, Kairui Song Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: A0FD0140007 X-Rspam-User: X-Rspamd-Server: rspam07 X-Stat-Signature: t8rrno7fi5cx9hwfxcmf7x5sbg511qnq X-HE-Tag: 1758171067-407554 X-HE-Meta: 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 VWEh4tzs p5T0aDvQWrSeYBgvVzmyE+GDPkhXfXF3hb+JVuRjCPWtj+a6IUUHXfCdhymjaEcyqaUbQyYpvkPM6Ab6W0Z91VknNeotkkoJVSdxM6TTPt/Qe0O6O2ZC2MGgeaN4w1qzmLylT+BlmFvum3Rs/niMEBpSd5qRhung8kcCG+TfO+a8RUBlCW/1mZUerI/FI9zbq61PCK/5hjW8XezP7qwBDka594eCONRt4O4EkukJCxQdCdGbHCqpBUK3gpGwMKZ4X6sTRTS6C7r/kizyxCs23A/EkZLHjRobwfWhuEQT+hdCZqNrMguQw3yJJkw== 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 17, 2025 at 4:50=E2=80=AFPM Barry Song <21cnbao@gmail.com> wrot= e: > > > Perhaps you could describe the swap table as similar to a PTE page tabl= e > > representing the swap cache mapping. > > That is correct for most 32-bit and 64-bit systems, > > but not for every machine. > > > > The only exception is a 32-bit system with a 64-bit physical address > > (Large Physical Address Extension, LPAE), which uses a 4 KB PTE table > > but a 2 KB swap table because the pointer is 32 bit while each page > > table entry is 64 bit. > > > > Maybe we can simply say that the number of entries in the swap table > > is the same as in a PTE page table? > > BTW, as Kairui mentioned, you plan to store the PFN instead of a > pointer in phase 2. Yes, let's update the document then and only then. Otherwise the document will be mismatching the code and confuse the reader. > > I wonder whether we need to switch to atomic64_t on systems where the > physical address is 64 bit but the virtual address is 32 bit :-) It is possible we need 64 bit for the swap cache anyway for other reasons when we get into the later phases. Again, let's deal with it later. Chris