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Mon, 12 Jan 2026 15:16:57 +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 GLLIJmkQZWn7FgAAD6G6ig (envelope-from ); Mon, 12 Jan 2026 15:16:57 +0000 From: Vlastimil Babka Date: Mon, 12 Jan 2026 16:16:58 +0100 Subject: [PATCH RFC v2 04/20] slab: add sheaves to most caches MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260112-sheaves-for-all-v2-4-98225cfb50cf@suse.cz> References: <20260112-sheaves-for-all-v2-0-98225cfb50cf@suse.cz> In-Reply-To: <20260112-sheaves-for-all-v2-0-98225cfb50cf@suse.cz> To: Harry Yoo , Petr Tesarik , Christoph Lameter , David Rientjes , Roman Gushchin Cc: Hao Li , Andrew Morton , Uladzislau Rezki , "Liam R. Howlett" , Suren Baghdasaryan , 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, Vlastimil Babka X-Mailer: b4 0.14.3 X-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 4D823C000B X-Stat-Signature: h99ob19np7r4rq5kicczbbjkmr6do8kz X-HE-Tag: 1768231031-551025 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: In the first step to replace cpu (partial) slabs with sheaves, enable sheaves for almost all caches. Treat args->sheaf_capacity as a minimum, and calculate sheaf capacity with a formula that roughly follows the formula for number of objects in cpu partial slabs in set_cpu_partial(). This should achieve roughly similar contention on the barn spin lock as there's currently for node list_lock without sheaves, to make benchmarking results comparable. It can be further tuned later. Don't enable sheaves for bootstrap caches as that wouldn't work. In order to recognize them by SLAB_NO_OBJ_EXT, make sure the flag exists even for !CONFIG_SLAB_OBJ_EXT. This limitation will be lifted for kmalloc caches after the necessary bootstrapping changes. Signed-off-by: Vlastimil Babka --- include/linux/slab.h | 6 ------ mm/slub.c | 51 +++++++++++++++++++++++++++++++++++++++++++++++---- 2 files changed, 47 insertions(+), 10 deletions(-) diff --git a/include/linux/slab.h b/include/linux/slab.h index 2482992248dc..2682ee57ec90 100644 --- a/include/linux/slab.h +++ b/include/linux/slab.h @@ -57,9 +57,7 @@ enum _slab_flag_bits { #endif _SLAB_OBJECT_POISON, _SLAB_CMPXCHG_DOUBLE, -#ifdef CONFIG_SLAB_OBJ_EXT _SLAB_NO_OBJ_EXT, -#endif _SLAB_FLAGS_LAST_BIT }; @@ -238,11 +236,7 @@ enum _slab_flag_bits { #define SLAB_TEMPORARY SLAB_RECLAIM_ACCOUNT /* Objects are short-lived */ /* Slab created using create_boot_cache */ -#ifdef CONFIG_SLAB_OBJ_EXT #define SLAB_NO_OBJ_EXT __SLAB_FLAG_BIT(_SLAB_NO_OBJ_EXT) -#else -#define SLAB_NO_OBJ_EXT __SLAB_FLAG_UNUSED -#endif /* * ZERO_SIZE_PTR will be returned for zero sized kmalloc requests. diff --git a/mm/slub.c b/mm/slub.c index 8ffeb3ab3228..6e05e3cc5c49 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -7857,6 +7857,48 @@ static void set_cpu_partial(struct kmem_cache *s) #endif } +static unsigned int calculate_sheaf_capacity(struct kmem_cache *s, + struct kmem_cache_args *args) + +{ + unsigned int capacity; + size_t size; + + + if (IS_ENABLED(CONFIG_SLUB_TINY) || s->flags & SLAB_DEBUG_FLAGS) + return 0; + + /* bootstrap caches can't have sheaves for now */ + if (s->flags & SLAB_NO_OBJ_EXT) + return 0; + + /* + * For now we use roughly similar formula (divided by two as there are + * two percpu sheaves) as what was used for percpu partial slabs, which + * should result in similar lock contention (barn or list_lock) + */ + if (s->size >= PAGE_SIZE) + capacity = 4; + else if (s->size >= 1024) + capacity = 12; + else if (s->size >= 256) + capacity = 26; + else + capacity = 60; + + /* Increment capacity to make sheaf exactly a kmalloc size bucket */ + size = struct_size_t(struct slab_sheaf, objects, capacity); + size = kmalloc_size_roundup(size); + capacity = (size - struct_size_t(struct slab_sheaf, objects, 0)) / sizeof(void *); + + /* + * Respect an explicit request for capacity that's typically motivated by + * expected maximum size of kmem_cache_prefill_sheaf() to not end up + * using low-performance oversize sheaves + */ + return max(capacity, args->sheaf_capacity); +} + /* * calculate_sizes() determines the order and the distribution of data within * a slab object. @@ -7991,6 +8033,10 @@ static int calculate_sizes(struct kmem_cache_args *args, struct kmem_cache *s) if (s->flags & SLAB_RECLAIM_ACCOUNT) s->allocflags |= __GFP_RECLAIMABLE; + /* kmalloc caches need extra care to support sheaves */ + if (!is_kmalloc_cache(s)) + s->sheaf_capacity = calculate_sheaf_capacity(s, args); + /* * Determine the number of objects per slab */ @@ -8595,15 +8641,12 @@ int do_kmem_cache_create(struct kmem_cache *s, const char *name, set_cpu_partial(s); - if (args->sheaf_capacity && !IS_ENABLED(CONFIG_SLUB_TINY) - && !(s->flags & SLAB_DEBUG_FLAGS)) { + if (s->sheaf_capacity) { s->cpu_sheaves = alloc_percpu(struct slub_percpu_sheaves); if (!s->cpu_sheaves) { err = -ENOMEM; goto out; } - // TODO: increase capacity to grow slab_sheaf up to next kmalloc size? - s->sheaf_capacity = args->sheaf_capacity; } #ifdef CONFIG_NUMA -- 2.52.0