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Thu, 30 Oct 2025 15:35:52 +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 +AqSG9iFA2n+YwAAD6G6ig (envelope-from ); Thu, 30 Oct 2025 15:35:52 +0000 Message-ID: <5e8e6e92-ba8f-4fee-bd01-39aacdd30dbe@suse.cz> Date: Thu, 30 Oct 2025 16:35:52 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC 10/19] slab: remove cpu (partial) slabs usage from allocation paths Content-Language: en-US To: Alexei Starovoitov Cc: Harry Yoo , Andrew Morton , Christoph Lameter , David Rientjes , Roman Gushchin , Uladzislau Rezki , "Liam R. Howlett" , Suren Baghdasaryan , Sebastian Andrzej Siewior , Alexei Starovoitov , linux-mm , LKML , linux-rt-devel@lists.linux.dev, bpf , kasan-dev References: <20251023-sheaves-for-all-v1-0-6ffa2c9941c0@suse.cz> <20251023-sheaves-for-all-v1-10-6ffa2c9941c0@suse.cz> <06241684-e056-40bd-88cc-0eb2d9d062bd@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-Stat-Signature: yz6kgs5utx3du6arfj7sp7pgkooetegs X-Rspamd-Queue-Id: 82CD020010 X-Rspamd-Server: rspam06 X-Rspam-User: X-HE-Tag: 1761838554-267094 X-HE-Meta: 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 nVc/Tne7 KQdAW3tlTVEqWfMoNxJbLKsCykbevPc51Cnel+wkrkvQuJXzpdrjTVaAIVuCE8tIAsYSP9JiMarDIAEtA9cpculxW1sd/TEkuejJqpTB7/Ic7U2TW4q1zBAjB076zR4BoIXEShQ5YJK1ybQC4TTHC6lCoHyKF7OEK5e6llOudZaCf6xNutjHURCRFOKvitWD+bGlZ9SHGPN8TYxz8V7S1U4zpasYo+eKxBQNX3G7/LOm6ElTkyqJjDrjiFLUIegB1OkBeFwo0Lqg2Hxcx3Y1eHdQWRweewV8QwY1IPiu5kxZ46NlbufmORa30s847aSo4XXEUYCW4Xn+YGF+BNmn2YDvD85/rw6g+aNj3KE4r0fgJQ+6y1Z3Wf14MxPzDQCmWGu5r 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 10/30/25 16:27, Alexei Starovoitov wrote: > On Thu, Oct 30, 2025 at 6:09 AM Vlastimil Babka wrote: >> >> On 10/30/25 05:32, Harry Yoo wrote: >> > On Thu, Oct 23, 2025 at 03:52:32PM +0200, Vlastimil Babka wrote: >> >> diff --git a/mm/slub.c b/mm/slub.c >> >> index e2b052657d11..bd67336e7c1f 100644 >> >> --- a/mm/slub.c >> >> +++ b/mm/slub.c >> >> @@ -4790,66 +4509,15 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node, >> >> >> >> stat(s, ALLOC_SLAB); >> >> >> >> - if (IS_ENABLED(CONFIG_SLUB_TINY) || kmem_cache_debug(s)) { >> >> - freelist = alloc_single_from_new_slab(s, slab, orig_size, gfpflags); >> >> - >> >> - if (unlikely(!freelist)) >> >> - goto new_objects; >> >> - >> >> - if (s->flags & SLAB_STORE_USER) >> >> - set_track(s, freelist, TRACK_ALLOC, addr, >> >> - gfpflags & ~(__GFP_DIRECT_RECLAIM)); >> >> - >> >> - return freelist; >> >> - } >> >> - >> >> - /* >> >> - * No other reference to the slab yet so we can >> >> - * muck around with it freely without cmpxchg >> >> - */ >> >> - freelist = slab->freelist; >> >> - slab->freelist = NULL; >> >> - slab->inuse = slab->objects; >> >> - slab->frozen = 1; >> >> - >> >> - inc_slabs_node(s, slab_nid(slab), slab->objects); >> >> + freelist = alloc_single_from_new_slab(s, slab, orig_size, gfpflags); >> >> >> >> - if (unlikely(!pfmemalloc_match(slab, gfpflags) && allow_spin)) { >> >> - /* >> >> - * For !pfmemalloc_match() case we don't load freelist so that >> >> - * we don't make further mismatched allocations easier. >> >> - */ >> >> - deactivate_slab(s, slab, get_freepointer(s, freelist)); >> >> - return freelist; >> >> - } >> >> + if (unlikely(!freelist)) >> >> + goto new_objects; >> > >> > We may end up in an endless loop in !allow_spin case? >> > (e.g., kmalloc_nolock() is called in NMI context and n->list_lock is >> > held in the process context on the same CPU) >> > >> > Allocate a new slab, but somebody is holding n->list_lock, so trylock fails, >> > free the slab, goto new_objects, and repeat. >> >> Ugh, yeah. However, AFAICS this possibility already exists prior to this >> patch, only it's limited to SLUB_TINY/kmem_cache_debug(s). But we should fix >> it in 6.18 then. >> How? Grab the single object and defer deactivation of the slab minus one >> object? Would work except for kmem_cache_debug(s) we open again a race for >> inconsistency check failure, and we have to undo the simple slab freeing fix >> and handle the accounting issue differently again. >> Fail the allocation for the debug case to avoid the consistency check >> issues? Would it be acceptable for kmalloc_nolock() users? > > You mean something like: > diff --git a/mm/slub.c b/mm/slub.c > index a8fcc7e6f25a..e9a8b75f31d7 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -4658,8 +4658,11 @@ static void *___slab_alloc(struct kmem_cache > *s, gfp_t gfpflags, int node, > if (kmem_cache_debug(s)) { > freelist = alloc_single_from_new_slab(s, slab, > orig_size, gfpflags); > > - if (unlikely(!freelist)) > + if (unlikely(!freelist)) { > + if (!allow_spin) > + return NULL; > goto new_objects; > + } > > or I misunderstood the issue? Yeah that would be the easiest solution, if you can accept the occasional allocation failures.