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Mon, 19 Jan 2026 09:34:08 +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 QpVoBpD6bWn1WAAAD6G6ig (envelope-from ); Mon, 19 Jan 2026 09:34:08 +0000 Message-ID: <4f60e230-c76e-4ab3-a0f0-7598dcb15d1a@suse.cz> Date: Mon, 19 Jan 2026 10:34:07 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 06/21] slab: introduce percpu sheaves bootstrap 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-v3-6-5595cb000772@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-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 23C40180004 X-Stat-Signature: dmo4mpdhppnjw6xbr8tsboqhzs44q9r4 X-Rspam-User: X-HE-Tag: 1768815249-903409 X-HE-Meta: U2FsdGVkX18HswPNyVhnXzYuyd+brwT/qUnhGaWSYzKkanhFokKg/SbsbONVP8iE4/nUVrHCq62UwY11rHdNxKTHRk1lONprZPplPu0aLSORuhpO1Dfp8tSHaClZYAXV0UVjkE4b9vAGT/ku8lwVFsqeDudwJolopWKdUUyZWt/sT4kHPh3iwTr4kV+4DzMyW2vq5uoE2cAFrq1C/9zsmcXDISc5OKDvj3s6GFqHhIKsvCt0NlNAkyZB/PCmm9v/vp+gHFP0cQfLbRMj37To+SK43IN3H1mmP/oVHyi/KwKhenQ8953x3scqMVFv9F1xK2mM7eVG2LPNEytNlil7zRxghTbDlzA9K/SBejfXVL3Q9+IWAVo+3LpHDaFGVHsq56j819Wb2AdlqW1Oggkdhz9MttJFz7sY2m1FHqv4okDPfo130zUSd6DiE7PXdzJmYMvreT3DsKGq0qtNMerNDdW88vGzX0Vmeqq2TTj+lKzy/9V2opnRCH7q+D6W83ZXOH/rZSy/bYKa3OLg/ELP4dap6evsHBbcjxLaoH/SR+H1CGABzega9nIm43Wvrifs813QMuhRfzjwaLBchEBBKPG1cbkHQyE9kcH2CD56sLg9j37FT4uUAMv7RjciruGt0EnrSjAM4fJT7F0O98QEK3ffHuBPW0gWpsGbxqbuWgs9xt5/JfouoVXMP0Zynvfy46QnyCHoCnBM7A2FffC+Iez4YSYQEW4AS92r9PwnrZd//5ieNu28fJQ0NnOL1wHp6/hajsE3XVdqwSunhrY/f7FeaOejx6CtEFIaeOQMOMBE34XwWiijX22+LI22qqU6JI/GXNWw9O0ZHJaQbUcN9G3XuvX8eqhHxGRtC55UoTo8gn1Z/QFc3yXClnlBgcDLvOj3FC1kkxj/+Xu3pbItNIMnMTwYxBKOhmHL90T+jmd+lVym9KIXWMcoAfPsbrxyrMsKNlmsvnJ5N0fRFkW tHt8vmzV UH5AMFtCOxg1+s84GN7RkVkNSnk+/bhq9RMi3rstx420WESRjiLTZSdWgPXO/rqbjGGQ1gK+ZJXLMvNqeoKqG4HL6W+iQVeAbeBTkH8DdrCkXwolA+qOSofFi8kWacVGKBGpV+OS4bZoTjYZ7JPfDzVW5B4VeCauFBVU+6tQSLvpLIKv6tpbjnm3w2HiEbh+4XddG0CDImszT86Fpl3I7NgP24JFP6Wuh8elW1c0wwaZVII3WnMxfP4icyNQTQbory4PDR+qaCcgZiV3lk7F5kwDKiT1l/awht2u0KZlDo54XPsUlIrT1Br0EpQ== 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 1/17/26 03:11, Suren Baghdasaryan wrote: > On Fri, Jan 16, 2026 at 2:40 PM Vlastimil Babka wrote: >> Thus sharing the single bootstrap sheaf like this for multiple caches >> and cpus is safe. >> >> Signed-off-by: Vlastimil Babka >> --- >> mm/slub.c | 119 ++++++++++++++++++++++++++++++++++++++++++-------------------- >> 1 file changed, 81 insertions(+), 38 deletions(-) >> >> diff --git a/mm/slub.c b/mm/slub.c >> index edf341c87e20..706cb6398f05 100644 >> --- a/mm/slub.c >> +++ b/mm/slub.c >> @@ -501,6 +501,18 @@ struct kmem_cache_node { >> struct node_barn *barn; >> }; >> >> +/* >> + * Every cache has !NULL s->cpu_sheaves but they may point to the >> + * bootstrap_sheaf temporarily during init, or permanently for the boot caches >> + * and caches with debugging enabled, or all caches with CONFIG_SLUB_TINY. This >> + * helper distinguishes whether cache has real non-bootstrap sheaves. >> + */ >> +static inline bool cache_has_sheaves(struct kmem_cache *s) >> +{ >> + /* Test CONFIG_SLUB_TINY for code elimination purposes */ >> + return !IS_ENABLED(CONFIG_SLUB_TINY) && s->sheaf_capacity; >> +} >> + >> static inline struct kmem_cache_node *get_node(struct kmem_cache *s, int node) >> { >> return s->node[node]; >> @@ -2855,6 +2867,10 @@ static void pcs_destroy(struct kmem_cache *s) >> if (!pcs->main) >> continue; >> >> + /* bootstrap or debug caches, it's the bootstrap_sheaf */ >> + if (!pcs->main->cache) >> + continue; > > I wonder why we can't simply check cache_has_sheaves(s) at the > beginning and skip the loop altogether. > I realize that __kmem_cache_release()->pcs_destroy() is called in the > failure path of do_kmem_cache_create() and s->cpu_sheaves might be > partially initialized if alloc_empty_sheaf() fails somewhere in the > middle of the loop inside init_percpu_sheaves(). But for that, > s->sheaf_capacity should still be non-zero, so checking > cache_has_sheaves() at the beginning of pcs_destroy() should still > work, no? I think it should, will do. > BTW, I see one last check for s->cpu_sheaves that you didn't replace > with cache_has_sheaves() inside __kmem_cache_release(). I think that's > because it's also in the failure path of do_kmem_cache_create() and > it's possible that s->sheaf_capacity > 0 while s->cpu_sheaves == NULL > (if alloc_percpu(struct slub_percpu_sheaves) fails). It might be > helpful to add a comment inside __kmem_cache_release() to explain why > cache_has_sheaves() can't be used there. The reason is rather what Harry said. I'll move the check to pcs_destroy() and add comment there. diff --git a/mm/slub.c b/mm/slub.c index 706cb6398f05..6b19aa518a1a 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -2858,19 +2858,26 @@ static void pcs_destroy(struct kmem_cache *s) { int cpu; + /* + * We may be unwinding cache creation that failed before or during the + * allocation of this. + */ + if (!s->cpu_sheaves) + return; + + /* pcs->main can only point to the bootstrap sheaf, nothing to free */ + if (!cache_has_sheaves(s)) + goto free_pcs; + for_each_possible_cpu(cpu) { struct slub_percpu_sheaves *pcs; pcs = per_cpu_ptr(s->cpu_sheaves, cpu); - /* can happen when unwinding failed create */ + /* This can happen when unwinding failed cache creation. */ if (!pcs->main) continue; - /* bootstrap or debug caches, it's the bootstrap_sheaf */ - if (!pcs->main->cache) - continue; - /* * We have already passed __kmem_cache_shutdown() so everything * was flushed and there should be no objects allocated from @@ -2889,6 +2896,7 @@ static void pcs_destroy(struct kmem_cache *s) } } +free_pcs: free_percpu(s->cpu_sheaves); s->cpu_sheaves = NULL; } @@ -5379,6 +5387,9 @@ kmem_cache_prefill_sheaf(struct kmem_cache *s, gfp_t gfp, unsigned int size) struct slab_sheaf *sheaf = NULL; struct node_barn *barn; + if (unlikely(!size)) + return NULL; + if (unlikely(size > s->sheaf_capacity)) { sheaf = kzalloc(struct_size(sheaf, objects, size), gfp); @@ -7833,8 +7844,7 @@ static void free_kmem_cache_nodes(struct kmem_cache *s) void __kmem_cache_release(struct kmem_cache *s) { cache_random_seq_destroy(s); - if (s->cpu_sheaves) - pcs_destroy(s); + pcs_destroy(s); #ifdef CONFIG_PREEMPT_RT if (s->cpu_slab) lockdep_unregister_key(&s->lock_key);