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Wed, 10 Sep 2025 15:46:29 -0700 (PDT) Date: Wed, 10 Sep 2025 15:46:29 -0700 (PDT) From: "Christoph Lameter (Ampere)" To: "Matthew Wilcox (Oracle)" cc: Vlastimil Babka , Andrew Morton , David Rientjes , Roman Gushchin , Harry Yoo , linux-mm@kvack.org Subject: Re: [PATCH v2 06/22] slab: Reimplement page_slab() In-Reply-To: <20250910115507.1991829-7-willy@infradead.org> Message-ID: <8eefb8ca-e310-48d4-0c3a-fa80665cab87@gentwo.org> References: <20250910115507.1991829-1-willy@infradead.org> <20250910115507.1991829-7-willy@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Stat-Signature: nu6cwkygree9h5oojyxyopyjnnqbof9h X-Rspamd-Queue-Id: 56EF820008 X-Rspam-User: X-Rspamd-Server: rspam03 X-HE-Tag: 1757544390-569731 X-HE-Meta: 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 CWkpon+O DuEJ2vljmIhXDDFNb9iXgzRz7RmEFovDaENt+9VPO+UtFYqj+t+BnIe4EjoV7nuRDzw2WWggI++XlN6eu4Z20LLyNmLhu45cSxuAcS2dOR4E4NpyZLOBu+bGi19+Hgm7UE+xbs7UpuWRjIx6C1QHIa2JZM51B7NY5ArPkqDAqVTF18ksw0G7I5iahsu8VFSxdHWsFBIWzbq+NQIt8Tu3yNAMohExeO5ZXYTXbc2sj1wXfTAPlgmr2ho8vgvHpa8ctDvPDzhn+CCvZ9RBHk/QWfusEzynHTFA3xSvH 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, 10 Sep 2025, Matthew Wilcox (Oracle) wrote: > In order to separate slabs from folios, we need to convert from any page > in a slab to the slab directly without going through a page to folio > conversion first. page_slab() is a little different from other memdesc > converters we have in that it will return NULL if the page is not part > of a slab. This will be the normal style for memdesc converters in > the future. We are looking forward to another level of indirection in order to get to struct slab? > -#define page_slab(p) (_Generic((p), \ > - const struct page *: (const struct slab *)(p), \ > - struct page *: (struct slab *)(p))) > +static inline struct slab *page_slab(const struct page *page) > +{ > + unsigned long head; > + > + head = READ_ONCE(page->compound_head); > + if (head & 1) > + page = (struct page *)(head - 1); > + if (data_race(page->page_type >> 24) != PGTY_slab) > + page = NULL; > + > + return (struct slab *)page; > +} compound_head() is open coded in there.