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From: Kent Overstreet To: Matthew Wilcox Cc: linux-mm@kvack.org, Vlastimil Babka , Andrew Morton , Christoph Lameter , Pekka Enberg , David Rientjes , Roman Gushchin , Hyeonggon Yoo <42.hyeyoo@gmail.com> Subject: Re: [PATCH] mm/slub: Make __ksize() faster Message-ID: <6iv6cmclbkx4vrhpohjlg6r3pf7cf3nsgiydycmsmlhsrjo4bd@bohvkgia6wyx> References: <20240308031325.218676-1-kent.overstreet@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Rspamd-Queue-Id: B205A160022 X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: 17jhhqy4i7dgacroqxgtykb6969ya7wz X-HE-Tag: 1709915260-449373 X-HE-Meta: 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 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, Mar 08, 2024 at 02:58:48PM +0000, Matthew Wilcox wrote: > On Fri, Mar 08, 2024 at 12:16:09AM -0500, Kent Overstreet wrote: > > On Fri, Mar 08, 2024 at 04:48:11AM +0000, Matthew Wilcox wrote: > > > On Thu, Mar 07, 2024 at 10:13:22PM -0500, Kent Overstreet wrote: > > > > This steals it to make __ksize() faster; it's now a single dependent > > > > load, instead of two. This is going to be important for tracking the > > > > amount of memory stranded by RCU, which we want to be able to do if > > > > we're going to be freeing all pagecache folios (and perhaps all folios) > > > > via RCU. > > > > > > Do you have any measurements? I don't necessarily object, it's just > > > that I would have thought we were already bringing slab->slab_cache > > > into cache as part of the freeing operation. > > > > for kfree() yes, but for kfree_rcu() no - that'll happen significantly > > later. > > > > I don't have measurements that it /matters/, but since we have the u32 > > there now this seems like a good use for it. > > There are potentiually better uses for those bits. We could turn > folio_test_slab() into a PageType test, freeing up a page flag. They overlap _mapcount, did you figure out how to use that for a PageType enum?