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b=QjvgL409U++4546oq4u2khWxMjwP4nVSl578yOHefIw0n8w7rvouTst69VWHN5niE tWiWKtBYrN8EZ64eHoPvq1VbruRDIC2jUrKzY8HdgI0ZETQ9/FEADVQq4dRZ0VL+S6 Itcdmqaaq2pa0th6qP/SIGGHiCjLUaAO16fILn2gr9QvCNRjPvMkpi3NKpgFr9SWET +nh+UwA/ZaCzgA5Ebe+jGkJx6uL0wKqH97qxsFlEfXauR4EOlpVKDDbYnYD/0HPhHC JJ5FWFEvV9JfUkdIRA6rpqGzbtJfg545JpTzbNsFk+muOGPI+9deNsuw7xGj5k/CQt VIIizZfTtaWuA== From: "Vlastimil Babka (SUSE)" Date: Sat, 24 Oct 2026 21:07:23 +0200 Subject: [PATCH RFC v2 1/8] mm, slab: refactor slab_min/max_order handling X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20261024-slub_tiny_rework-v2-1-bf1419ab5ffd@kernel.org> References: <20261024-slub_tiny_rework-v2-0-bf1419ab5ffd@kernel.org> In-Reply-To: <20261024-slub_tiny_rework-v2-0-bf1419ab5ffd@kernel.org> To: Harry Yoo Cc: Hao Li , Christoph Lameter , David Rientjes , Roman Gushchin , Geert Uytterhoeven , Conor Dooley , Damien Le Moal , linux-mm@kvack.org, linux-kernel@vger.kernel.org, "Vlastimil Babka (SUSE)" X-Mailer: b4 0.16.0 X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 8470D100003 X-Spam-Status: No, score=-19.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=4.0.1 X-Stat-Signature: dr1aprajn79romf138wcncd16rsnmj83 X-HE-Tag: 1792868859-627782 X-HE-Meta: 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 AouxKt3R hDwy93+jy6Z4ucMB1ECR+Jm7RRNPr8kZahg8jQRWsdscemWsIWkmTCvDFfoMpb6hyhJmf8WDJlbn/0FD6kLzMZAJ/1wfXxtGzucDcv1vDr0+po8bNMap4wd9k3syxMw9/5Z6LyKKR1gP9/Y2OWmiqQClcmyYesl39V2AyaK5sLXh3tpPYt2SARK0Asv8cwcvBXYSyjybJGH5X72bimTJF4Ol46LRy/B8UbRrYhn+ykpj130h7mf+Bw7kAKM2aVbymMDK6lQ0bqKNvu6EHu80oWIHxyk1QLBqGCr5i Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 Setting slab_min_order and slab_max_order as boot-time parameters currently has several not so great aspects: - slab_min_order is not checked against MAX_PAGE_ORDER - slab_min_order can raise slab_max_order - processing requires custom callbacks, their execution order depends on the order of boot time parameters specified - upcoming SLUB_TINY changes would be more complicated Instead of custom callbacks, introduce __initdata variables that hold the boot-time parameter values (if given). All inputs are then evaluated deterministically in kmem_cache_init(). slab_min_order is always capped at slab_max_order and cannot raise it. debug_guardpage_minorder() still overrides any given boot time params, but it could be changed if there's a use case. While at it, rename the slub_min/max_order variables and slub_min_objects to have a "slab_" prefix instead, as their values determine the sizing of slabs, and the "slub_" prefix already became deprecated also for the boot-time parameters. Signed-off-by: Vlastimil Babka (SUSE) --- mm/slub.c | 84 ++++++++++++++++++++++++--------------------------------------- 1 file changed, 32 insertions(+), 52 deletions(-) diff --git a/mm/slub.c b/mm/slub.c index 45e077c7526c..30714557306d 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -7684,10 +7684,17 @@ EXPORT_SYMBOL(kmem_cache_alloc_bulk_noprof); * and increases the number of allocations possible without having to * take the list_lock. */ -static unsigned int slub_min_order; -static unsigned int slub_max_order = +static unsigned int slab_min_order; +static unsigned int slab_max_order = IS_ENABLED(CONFIG_SLUB_TINY) ? 1 : PAGE_ALLOC_COSTLY_ORDER; -static unsigned int slub_min_objects; +static unsigned int slab_min_objects; + +/* + * Store values set by boot-time parameters, to be evaluated in + * kmem_cache_init(). UINT_MAX means they were not set, as 0 is a valid value. + */ +static unsigned int slab_min_order_param __initdata = UINT_MAX; +static unsigned int slab_max_order_param __initdata = UINT_MAX; /* * Calculate the order of allocation given an slab object size. @@ -7741,7 +7748,7 @@ static inline int calculate_order(unsigned int size) unsigned int max_objects; unsigned int min_order; - min_objects = slub_min_objects; + min_objects = slab_min_objects; if (!min_objects) { /* * Some architectures will only update present cpus when @@ -7758,10 +7765,10 @@ static inline int calculate_order(unsigned int size) min_objects = 4 * (fls(nr_cpus) + 1); } /* min_objects can't be 0 because get_order(0) is undefined */ - max_objects = max(order_objects(slub_max_order, size), 1U); + max_objects = max(order_objects(slab_max_order, size), 1U); min_objects = min(min_objects, max_objects); - min_order = max_t(unsigned int, slub_min_order, + min_order = max_t(unsigned int, slab_min_order, get_order(min_objects * size)); if (order_objects(min_order, size) > MAX_OBJS_PER_PAGE) return get_order(size * MAX_OBJS_PER_PAGE) - 1; @@ -7782,9 +7789,9 @@ static inline int calculate_order(unsigned int size) * long as at least single object fits within slab_max_order. */ for (unsigned int fraction = 16; fraction > 1; fraction /= 2) { - order = calc_slab_order(size, min_order, slub_max_order, + order = calc_slab_order(size, min_order, slab_max_order, fraction); - if (order <= slub_max_order) + if (order <= slab_max_order) return order; } @@ -8355,50 +8362,14 @@ void __kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct slab *slab) * Kmalloc subsystem *******************************************************************/ -static int __init setup_slub_min_order(const char *str, const struct kernel_param *kp) -{ - int ret; - - ret = kstrtouint(str, 0, &slub_min_order); - if (ret) - return ret; +core_param(slab_min_order, slab_min_order_param, uint, 0); +core_param(slub_min_order, slab_min_order_param, uint, 0); - if (slub_min_order > slub_max_order) - slub_max_order = slub_min_order; +core_param(slab_max_order, slab_max_order_param, uint, 0); +core_param(slub_max_order, slab_max_order_param, uint, 0); - return 0; -} - -static const struct kernel_param_ops param_ops_slab_min_order __initconst = { - .set = setup_slub_min_order, -}; -__core_param_cb(slab_min_order, ¶m_ops_slab_min_order, &slub_min_order, 0); -__core_param_cb(slub_min_order, ¶m_ops_slab_min_order, &slub_min_order, 0); - -static int __init setup_slub_max_order(const char *str, const struct kernel_param *kp) -{ - int ret; - - ret = kstrtouint(str, 0, &slub_max_order); - if (ret) - return ret; - - slub_max_order = min_t(unsigned int, slub_max_order, MAX_PAGE_ORDER); - - if (slub_min_order > slub_max_order) - slub_min_order = slub_max_order; - - return 0; -} - -static const struct kernel_param_ops param_ops_slab_max_order __initconst = { - .set = setup_slub_max_order, -}; -__core_param_cb(slab_max_order, ¶m_ops_slab_max_order, &slub_max_order, 0); -__core_param_cb(slub_max_order, ¶m_ops_slab_max_order, &slub_max_order, 0); - -core_param(slab_min_objects, slub_min_objects, uint, 0); -core_param(slub_min_objects, slub_min_objects, uint, 0); +core_param(slab_min_objects, slab_min_objects, uint, 0); +core_param(slub_min_objects, slab_min_objects, uint, 0); #ifdef CONFIG_NUMA static int __init setup_slab_strict_numa(const char *str, const struct kernel_param *kp) @@ -8771,8 +8742,17 @@ void __init kmem_cache_init(void) slab_obj_ext_has_codetag_init(); + if (slab_max_order_param <= MAX_PAGE_ORDER) + slab_max_order = slab_max_order_param; + + if (slab_min_order_param <= MAX_PAGE_ORDER) + slab_min_order = slab_min_order_param; + if (debug_guardpage_minorder()) - slub_max_order = 0; + slab_max_order = 0; + + if (slab_min_order > slab_max_order) + slab_min_order = slab_max_order; /* Inform pointer hashing choice about slub debugging state. */ hash_pointers_finalize(__slub_debug_enabled()); @@ -8823,7 +8803,7 @@ void __init kmem_cache_init(void) pr_info("SLUB: HWalign=%d, Order=%u-%u, MinObjects=%u, CPUs=%u, Nodes=%u\n", cache_line_size(), - slub_min_order, slub_max_order, slub_min_objects, + slab_min_order, slab_max_order, slab_min_objects, nr_cpu_ids, nr_node_ids); } -- 2.56.0