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Received: from willy by casper.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1uObsq-00000008DjY-2u1O; Mon, 09 Jun 2025 12:45:48 +0000 Date: Mon, 9 Jun 2025 13:45:48 +0100 From: Matthew Wilcox To: Harry Yoo Cc: Vlastimil Babka , Christoph Lameter , David Rientjes , linux-mm@kvack.org Subject: Re: [PATCH 02/10] slab: Rename slab->__page_flags to slab->flags Message-ID: References: <20250606222214.1395799-1-willy@infradead.org> <20250606222214.1395799-3-willy@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Rspamd-Queue-Id: 21A41120009 X-Stat-Signature: 19pc9rqkpnqjgpji9nf4j7mxxwam4nnk X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1749473154-681784 X-HE-Meta: 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 B0LJZeYE dDl+XXEprxL6cgL8mO3FNImYRBPv6BPWbdWzPbSOMzuA7a0vuy7re4YkV+xoHwzhmXHh5VVrDCU3bft/mwFA972xmuwsdX8iNwJY6YRAgVeBPvfM8F0kOfCeV5jUY3wq7wJHnSFlZE+XlRVjG1BjBce/83rJoReT0xeDWLVfHe5g1hob68q5WjMJUjLLhefNhaUzCAGohGQlKOb9aoQxBgSpcox+TGDUIbsl2sBfAwclS3ocQ7PrH+OYBi5yQ4KHXrRZOZcZIq848OjXfTB+27J+7G9JlstkHealrSeZ+lCmmoLk= 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 Mon, Jun 09, 2025 at 11:15:07AM +0900, Harry Yoo wrote: > > +/** > > + * enum slab_flags - How the slab flags bits are used. > > + * @SL_locked: Is locked with slab_lock() > > + * > > + * The slab flags share space with the page flags but some bits have > > + * different interpretations. The high bits are used for information > > + * like zone/node/section. > > + */ > > +enum slab_flags { > > + SL_locked, > > +}; > > I think we need to make sure SL_locked use the same bit as PG_locked > at least for now? > > I'm not sure what prevents the MM code from checking page flags on a slab > and getting confused by the SL_locked bit is set. The lock bit is actually used very differently between page lock and slab lock. If there is any code inadvertently checking one when it's looking for the other, it's already broken. I can't think of anywhere which would look for it; we're pretty fastidious about checking for is_slab() before going anywhere near the lock bit. > Or the other way around—a slab might have a page flag (e.g., PG_head) set > and mistakenly interpret it as SL_locked. PG_head is a good one, but I don't think we're going to run into it before we finish the page diet.