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Tue, 16 Sep 2025 21:50:54 -0700 (PDT) MIME-Version: 1.0 References: <20250916160100.31545-1-ryncsn@gmail.com> <20250916160100.31545-16-ryncsn@gmail.com> In-Reply-To: From: Barry Song <21cnbao@gmail.com> Date: Wed, 17 Sep 2025 12:50:42 +0800 X-Gm-Features: AS18NWCiSnRJzKpUj8fDfFvjwQx63dGbAKROP5LujvWrwk9OWlY3tSO08qEUO-A Message-ID: Subject: Re: [PATCH v4 15/15] mm, swap: use a single page for swap table when the size fits To: Kairui Song Cc: linux-mm@kvack.org, Andrew Morton , Matthew Wilcox , Hugh Dickins , Chris Li , 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 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: DDE0A1C0008 X-Stat-Signature: 9jzdunqxobzd3n86cz7i4b8z5gf9gckf X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1758084655-726851 X-HE-Meta: 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 EJsbh0d6 MfT+Pay0rFHnmHhk62i1PTikFh5PmyiFbEdK1DGFPyj8aKCT5Nt/iX7GE4jZsHaA38UFyXvTSQIIoHgaCSXeA8thXnNQHbaMlXzZgcZgwj4fzobhAglPOAWKjko+0N2PAX6ucZLKgm7TQlndC9BR3heDhQ2d+0ma4oYgnHVfZOFZebvu1Ahfqh2UHR3fbZQeUipnUyIgSvY0fFusOqZbdNyD1CAnChWjQuBs0zcmouElORZ6DY2YFc48hcrlZKK/gEVnrz8A8ABjv6mCbkRoGBefz8FuZ0nbsfSxqAhM0zouPnmCIcOhiJfiD4/mcNfsY/m0taAtIUqz7uR2A8/gsVVs+RRDby3/34YLW8O+MJOZGlEhWj2Gq9XuhWID7pvsnkU4MM+T8KbVC19+8wYlseuQfl2LcE9ik1UkPMcpq+NF0O4GayA9GFh7wpnaHCp9Z8ZK1h0C6tYbjhe858pZ3tlD6aqqndhN8iK+4PBSKLCygoRY= 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 12:41=E2=80=AFPM Barry Song <21cnbao@gmail.com> wro= te: > > > > > > > > --- > > > > +static void swap_table_free(struct swap_table *table) > > > > +{ > > > > + if (!SWP_TABLE_USE_PAGE) { > > > > + kmem_cache_free(swap_table_cachep, table); > > > > + return; > > > > + } > > > > + > > > > + call_rcu(&(folio_page(virt_to_folio(table), 0)->rcu_head), > > > > + swap_table_free_folio_rcu_cb); > > > > +} > > > > > > Can=E2=80=99t it simply be: > > > virt_to_page(table)->rcu_head ? > > > > I'm not sure if we prefer folios when possible? > > Not sure either, but even Mathew still sometimes suggests using PAGE: > > https://lore.kernel.org/lkml/aLrrQDCBzaMwwmA-@casper.infradead.org/ > > BTW, "(folio_page(folio), 0)" looks quite strange. I mean, why is it 0 > instead of 1? > Although we know it=E2=80=99s always one PAGE, 0 still seems strange. I mean, we should always free an entire folio, right? It=E2=80=99s impossible to free just one page from a folio unless we split = a THP, etc. So it seems more correct that rcu_head should also be promoted to the folio= . /** @rcu_head: You can use this to free a folio by RCU. */ struct rcu_head rcu_head; Definitely outside the scope of this patchset, so not a blocker :-) > > > > > Either way is fine, they are identical for this use case. > > > Thanks Barry