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Wed, 21 Jan 2026 13:22:12 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id OTCoGQTTcGlWKAAAD6G6ig (envelope-from ); Wed, 21 Jan 2026 13:22:12 +0000 Message-ID: Date: Wed, 21 Jan 2026 14:22:12 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 09/21] slab: add optimized sheaf refill from partial list Content-Language: en-US To: Suren Baghdasaryan Cc: Harry Yoo , Petr Tesarik , Christoph Lameter , David Rientjes , Roman Gushchin , Hao Li , Andrew Morton , Uladzislau Rezki , "Liam R. Howlett" , Sebastian Andrzej Siewior , Alexei Starovoitov , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev, bpf@vger.kernel.org, kasan-dev@googlegroups.com References: <20260116-sheaves-for-all-v3-0-5595cb000772@suse.cz> <20260116-sheaves-for-all-v3-9-5595cb000772@suse.cz> From: Vlastimil Babka Autocrypt: addr=vbabka@suse.cz; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSBWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBzdXNlLmN6PsLBlAQTAQoAPgIbAwULCQgHAwUVCgkICwUWAgMBAAIe AQIXgBYhBKlA1DSZLC6OmRA9UCJPp+fMgqZkBQJnyBr8BQka0IFQAAoJECJPp+fMgqZkqmMQ AIbGN95ptUMUvo6aAdhxaOCHXp1DfIBuIOK/zpx8ylY4pOwu3GRe4dQ8u4XS9gaZ96Gj4bC+ jwWcSmn+TjtKW3rH1dRKopvC07tSJIGGVyw7ieV/5cbFffA8NL0ILowzVg8w1ipnz1VTkWDr 2zcfslxJsJ6vhXw5/npcY0ldeC1E8f6UUoa4eyoskd70vO0wOAoGd02ZkJoox3F5ODM0kjHu Y97VLOa3GG66lh+ZEelVZEujHfKceCw9G3PMvEzyLFbXvSOigZQMdKzQ8D/OChwqig8wFBmV QCPS4yDdmZP3oeDHRjJ9jvMUKoYODiNKsl2F+xXwyRM2qoKRqFlhCn4usVd1+wmv9iLV8nPs 2Db1ZIa49fJet3Sk3PN4bV1rAPuWvtbuTBN39Q/6MgkLTYHb84HyFKw14Rqe5YorrBLbF3rl M51Dpf6Egu1yTJDHCTEwePWug4XI11FT8lK0LNnHNpbhTCYRjX73iWOnFraJNcURld1jL1nV r/LRD+/e2gNtSTPK0Qkon6HcOBZnxRoqtazTU6YQRmGlT0v+rukj/cn5sToYibWLn+RoV1CE Qj6tApOiHBkpEsCzHGu+iDQ1WT0Idtdynst738f/uCeCMkdRu4WMZjteQaqvARFwCy3P/jpK uvzMtves5HvZw33ZwOtMCgbpce00DaET4y/UzsBNBFsZNTUBCACfQfpSsWJZyi+SHoRdVyX5 J6rI7okc4+b571a7RXD5UhS9dlVRVVAtrU9ANSLqPTQKGVxHrqD39XSw8hxK61pw8p90pg4G /N3iuWEvyt+t0SxDDkClnGsDyRhlUyEWYFEoBrrCizbmahOUwqkJbNMfzj5Y7n7OIJOxNRkB IBOjPdF26dMP69BwePQao1M8Acrrex9sAHYjQGyVmReRjVEtv9iG4DoTsnIR3amKVk6si4Ea X/mrapJqSCcBUVYUFH8M7bsm4CSxier5ofy8jTEa/CfvkqpKThTMCQPNZKY7hke5qEq1CBk2 wxhX48ZrJEFf1v3NuV3OimgsF2odzieNABEBAAHCwXwEGAEKACYCGwwWIQSpQNQ0mSwujpkQ PVAiT6fnzIKmZAUCZ8gcVAUJFhTonwAKCRAiT6fnzIKmZLY8D/9uo3Ut9yi2YCuASWxr7QQZ lJCViArjymbxYB5NdOeC50/0gnhK4pgdHlE2MdwF6o34x7TPFGpjNFvycZqccSQPJ/gibwNA zx3q9vJT4Vw+YbiyS53iSBLXMweeVV1Jd9IjAoL+EqB0cbxoFXvnjkvP1foiiF5r73jCd4PR rD+GoX5BZ7AZmFYmuJYBm28STM2NA6LhT0X+2su16f/HtummENKcMwom0hNu3MBNPUOrujtW khQrWcJNAAsy4yMoJ2Lw51T/5X5Hc7jQ9da9fyqu+phqlVtn70qpPvgWy4HRhr25fCAEXZDp xG4RNmTm+pqorHOqhBkI7wA7P/nyPo7ZEc3L+ZkQ37u0nlOyrjbNUniPGxPxv1imVq8IyycG AN5FaFxtiELK22gvudghLJaDiRBhn8/AhXc642/Z/yIpizE2xG4KU4AXzb6C+o7LX/WmmsWP Ly6jamSg6tvrdo4/e87lUedEqCtrp2o1xpn5zongf6cQkaLZKQcBQnPmgHO5OG8+50u88D9I rywqgzTUhHFKKF6/9L/lYtrNcHU8Z6Y4Ju/MLUiNYkmtrGIMnkjKCiRqlRrZE/v5YFHbayRD dJKXobXTtCBYpLJM4ZYRpGZXne/FAtWNe4KbNJJqxMvrTOrnIatPj8NhBVI0RSJRsbilh6TE m6M14QORSWTLRg== In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Action: no action X-Rspam-User: X-Stat-Signature: iq8xmtaca9zzssz4z7z1qd6o55edqss6 X-Rspamd-Queue-Id: DD9B3C000E X-Rspamd-Server: rspam05 X-HE-Tag: 1769001734-186114 X-HE-Meta: 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 kHJPxbhi E9KPRynJmAhNNkqFM3b0peN+LmE+i4XRgJ8iHqSvkE99iHEcM5VIlR5pmYQU+sj6uVzBePKr7eGJsdVTYPlt2iKalEYQZojOOVuOntc7hsjwYwKNQurn9Fd1Eve7yje1YdfAk844pVtX3gqIYws8ySD2UnclAEdULnPstDqDiJEMKeUY9ylqoaMyyZxy9aWt4tWlgz4TZ0oIge8qn0lQezdxAydctpzD6B0iQGjCT6DcMmKOW/DVa0R/9qAuruTKmpt+xdvVjYK89oLmgyPxZjK/O7c4REi0619G/h+EpNF0RC1IsbnN5wEyhc1/qJSi92upKtYVUoKaq1ZafT4iZe52G5Q== 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 1/20/26 18:19, Suren Baghdasaryan wrote: > On Fri, Jan 16, 2026 at 2:40 PM Vlastimil Babka wrote: >> >> At this point we have sheaves enabled for all caches, but their refill >> is done via __kmem_cache_alloc_bulk() which relies on cpu (partial) >> slabs - now a redundant caching layer that we are about to remove. >> >> The refill will thus be done from slabs on the node partial list. >> Introduce new functions that can do that in an optimized way as it's >> easier than modifying the __kmem_cache_alloc_bulk() call chain. >> >> Extend struct partial_context so it can return a list of slabs from the >> partial list with the sum of free objects in them within the requested >> min and max. >> >> Introduce get_partial_node_bulk() that removes the slabs from freelist >> and returns them in the list. >> >> Introduce get_freelist_nofreeze() which grabs the freelist without >> freezing the slab. >> >> Introduce alloc_from_new_slab() which can allocate multiple objects from >> a newly allocated slab where we don't need to synchronize with freeing. >> In some aspects it's similar to alloc_single_from_new_slab() but assumes >> the cache is a non-debug one so it can avoid some actions. >> >> Introduce __refill_objects() that uses the functions above to fill an >> array of objects. It has to handle the possibility that the slabs will >> contain more objects that were requested, due to concurrent freeing of >> objects to those slabs. When no more slabs on partial lists are >> available, it will allocate new slabs. It is intended to be only used >> in context where spinning is allowed, so add a WARN_ON_ONCE check there. >> >> Finally, switch refill_sheaf() to use __refill_objects(). Sheaves are >> only refilled from contexts that allow spinning, or even blocking. >> > > Some nits, but otherwise LGTM. > Reviewed-by: Suren Baghdasaryan Thanks. > > From the above code it seems like you are trying to get at least > pc->min_objects and as close as possible to the pc->max_objects > without exceeding it (with a possibility that we will exceed both > min_objects and max_objects in one step). Is that indeed the intent? > Because otherwise could could simplify these conditions to stop once > you crossed pc->min_objects. Yeah see my reply to Harry, it's for future tuning. >> + if (slab->freelist) { > > nit: It's a bit subtle that the checks for slab->freelist here and the > earlier one for ((slab->objects - slab->inuse) > count) are > effectively equivalent. That's because this is a new slab and objects > can't be freed into it concurrently. I would feel better if both > checks were explicitly the same, like having "bool extra_objs = > (slab->objects - slab->inuse) > count;" and use it for both checks. > But this is minor, so feel free to ignore. OK, doing this for your and Hao Li's comment: diff --git a/mm/slub.c b/mm/slub.c index d6fde1d60ae9..015bdef11eb6 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -4505,7 +4505,7 @@ static inline void *get_freelist(struct kmem_cache *s, struct slab *slab) * Assumes the slab is isolated from node partial list and not frozen. * * Assumes this is performed only for caches without debugging so we - * don't need to worry about adding the slab to the full list + * don't need to worry about adding the slab to the full list. */ static inline void *get_freelist_nofreeze(struct kmem_cache *s, struct slab *slab) { @@ -4569,10 +4569,17 @@ static unsigned int alloc_from_new_slab(struct kmem_cache *s, struct slab *slab, { unsigned int allocated = 0; struct kmem_cache_node *n; + bool needs_add_partial; unsigned long flags; void *object; - if (!allow_spin && (slab->objects - slab->inuse) > count) { + /* + * Are we going to put the slab on the partial list? + * Note slab->inuse is 0 on a new slab. + */ + needs_add_partial = (slab->objects > count); + + if (!allow_spin && needs_add_partial) { n = get_node(s, slab_nid(slab)); @@ -4594,7 +4601,7 @@ static unsigned int alloc_from_new_slab(struct kmem_cache *s, struct slab *slab, } slab->freelist = object; - if (slab->freelist) { + if (needs_add_partial) { if (allow_spin) { n = get_node(s, slab_nid(slab));