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Sat, 19 Apr 2025 19:46:03 -0700 (PDT) Received: from [2a00:79e0:2eb0:8:3e8e:d566:514d:339b] ([2a00:79e0:2eb0:8:3e8e:d566:514d:339b]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-22c50bf55d0sm40890315ad.86.2025.04.19.19.46.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 19 Apr 2025 19:46:03 -0700 (PDT) Date: Sat, 19 Apr 2025 19:46:02 -0700 (PDT) From: David Rientjes To: Harry Yoo cc: Vlastimil Babka , Matthew Wilcox , linux-mm@kvack.org, Christoph Lameter , Andrew Morton Subject: Re: [PATCH RFC] mm, slab: warn when increasing refcount on large kmalloc page In-Reply-To: <8da1a88e-0cbf-fa65-bca9-4843ceb0c8dd@google.com> Message-ID: <6486c5da-0d78-a400-33bd-c4b3cea13ba5@google.com> References: <20250417074102.4543-2-vbabka@suse.cz> <8da1a88e-0cbf-fa65-bca9-4843ceb0c8dd@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 0D3FC2000B X-Stat-Signature: i1dc9181a8pwotu5u1iae1efoukr4biy X-Rspam-User: X-HE-Tag: 1745117164-650341 X-HE-Meta: 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 h2hFBLWU ILfZfSlMT0Jct1sTekW5YQzfGcPIkJTw0wp4ehB2ld0SNzXvFRpwriQPvSKi180d6BHR/XolXE4r+FtYYQqjNYjQL+2FJ684g3XgV9SGcPJommDMtDgczP1D0uHTfyf/ZQ2Jl7qmbZDKjo3grjgTcSySrO00a56DqP9FVicVElxfDx37kub80bynAb1BL1TSeIuydiDjajzsxEHKL2gg1WrI4FJv2v6BcZ5mGFB8+1gjumOCIagKL8+4lMycEmNZ5hoOjEjqUt3ke+pnsnQyf7iJ6nXzfYaX1oPXCJEF9joFL03aaJ4X0y0G2FyXv60wMlUxiuGlcV83JQ+ZKeBSNWIxq6CUQAaD0F/fQHAPD8RNlVUg= 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 Sat, 19 Apr 2025, David Rientjes wrote: > > > Since slab pages are now frozen, increasing refcount on a page > > > containing a kmalloc() allocation is not possible anymore. Large kmalloc > > > pages should ideally behave the same, because the decision for which > > > allocation size to use them is the slab allocator's implementation > > > detail, and sizes passed to kmalloc() might depend on e.g. user input. > > > > Agreed. > > > > > Because of some unexpected fallout in the slab pages case (see commit > > > b9c0e49abfca ("mm: decline to manipulate the refcount on a slab page"), > > > let's take a more cautious approach and before making large kmalloc > > > pages actually frozen, start warning about code that would try to > > > increase refcount on them. > > > > > > Signed-off-by: Vlastimil Babka > > > --- > > > I'd like to expose this via slab-next and see if there are any reports. > > > If not for few weeks, maybe proceed immediately to freezing refcount and > > > handling it in get_page/put_page exactly like folio_test_slab. Thoughts? > > > > +1 > > > > Let's give testing a try. > > > > ...at least it does not hit anything on my box. > > > > Same, I ran this through a number of benchmarks on x86 and couldn't find > any occurrences of the warning. > Btw, the benchmarks that I normally run regularly on SLUB are kernbench, multichase, hackbench, specjbb, will-it-scale, redis, unixbench, netperf TCP_RR and UDP_STREAM, on both x86 and arm64. I haven't run on any other architectures recently, but perhaps others do. Are there any other benchmarks that people normally run for slab allocator related changes?