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Wed, 12 Nov 2025 15:56:19 +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 uWaTNyOuFGmwCwAAD6G6ig (envelope-from ); Wed, 12 Nov 2025 15:56:19 +0000 Message-ID: <4b72bcad-5174-49c7-ad90-63a9c312df0b@suse.cz> Date: Wed, 12 Nov 2025 16:56:19 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 7/7] mempool: add mempool_{alloc,free}_bulk Content-Language: en-US To: Christoph Hellwig Cc: Andrew Morton , Christoph Lameter , David Rientjes , Roman Gushchin , Harry Yoo , Eric Biggers , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20251111135300.752962-1-hch@lst.de> <20251111135300.752962-8-hch@lst.de> <20251112154754.GB7209@lst.de> 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: <20251112154754.GB7209@lst.de> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Action: no action X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: A27271A0013 X-Stat-Signature: ha9kmkh6mk4jr9tinb1qdyrftjh9gcsb X-Rspam-User: X-HE-Tag: 1762962982-44925 X-HE-Meta: U2FsdGVkX18eSeRoWYPDrrJ/USayBLauY792l+//XV8BVkZOO1XK3fKMzibovy4D+t7RBTWIK0lNSZHCyNLfRbFA8y0ySL/odUmK7fCPJ/WGh8nfukMtAx6sSyHmr/VluiOXUXMyqWkLBgv5SrneKVqcTTe7Zr6qZ6pyjF2kSkQ0MTrQ2YwGkCgeS97m5gNFvqHLF5/XHf+ej161AOkeLVm37w/v+eVjuMSBlQsiMw2ow1ul480OthE2QF/rXdiorw0JX1x8NJMw/miyNbq8n792nz3WbcGSGtz0wODLVzvJgGTbMNwsZ8mP0PzziqF+uNHBJBOPdu6U+JmxKmaK7gpgMSXlZfmK2HAC5WMZlQQp1m3Wsxbk0rp7kAcAkWaIVvt6xn9soSou1bsObCPBn2Ds7hRpUMPm19Egrp9t68eAWojvsp4k3Deh+GI7L1iO1OO3kFr3AGlnrIxXv/9TmSvth9huPPbBZKgJrFpMfrbIcQ/mcSRAuHF9F7hFw6NbADL7rlfymbYnofUQJmxplmM9oYcARhd3iS0DSJSMwlozvWyomxb5yBKywWkXPYUhX0IgRUvtENv9Vm+fZVez6XdpgvoOMGDnh93kc9EeoEEo8oclqqWPObxgQDLPaaHwk4ABSh0Nokrh5IDVxGRSJnRoDEHrA+W+Va/WdBKEXFXwnyA9LRMMeKYA3Z/qPu06D+qG7wGuRxS4ZPk4q3InlIcfRbg+Wpz3BtxWT0lYgwREaZmbQ/fSLxn34Q3qqlS+OQT5zOTty7H74h3N5AXmxyx6jzBZptEGZswx/HdhO8KU9tm2aUoibx6yOnsGyZGZZyNh/vphKrSMvsIe4tc/uiD1hlJLNv+uOhmZbZ7GCw4gbaBE/i6+XiNPH7ziwFcCeVbZA5vTVX/YR9VAZuTTneSvAJHCrcQ4EyiT5U5cTVubhMu2pcQev9MyAAsv8K6gcPnR0GRIgeMOtWcFRoU SzqEelGb rOD8h6QmWtvM90uJ5TkuDcmqd//hboEMwcwIXaP4Meo7CJegDgOUY5K7qOad5rH1guoaxq4dXT13ew1wpTKcETtHpG9Vm6gJC25Zf66fcKCOZd7fK1a+c1n7FG/1KVIrx/Tb2llD8LRRsaTEUy97fdMTCNyFrEqlZjp9QaiEo051MbTMX5HLMyGq2Y3VPHDY5Izjvyo0+l3n4S08vWrxEogwqujNFeYPrjdG3uslxcqpABSqsMvfZ7q0NDt4+4w+FrNi6tv8osateF99E9QRr1d+ekCm8g+VS9Ts21rFa5PmAodJgdGhNzypfo10P2tjb9t5P8dpf6pYcktQ= 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 11/12/25 16:47, Christoph Hellwig wrote: > On Wed, Nov 12, 2025 at 01:20:21PM +0100, Vlastimil Babka wrote: >> > + if (IS_ERR(fault_create_debugfs_attr("fail_mempool_alloc", NULL, >> > + &fail_mempool_alloc)) || >> > + IS_ERR(fault_create_debugfs_attr("fail_mempool_alloc_bulk", NULL, >> > + &fail_mempool_alloc_bulk))) >> > + return -ENOMEM; >> >> Pedantically speaking the error (from debugfs_create_dir()) might be >> different, probably doesn't matter in practice. > > Yeah, this is an initcall, so the exact error really does not matter. > But adding an error variable isn't that annyoing, so I'll switch to > that. > >> > unsigned long flags; >> > - void *element; >> > + unsigned int i; >> > >> > spin_lock_irqsave(&pool->lock, flags); >> > - if (unlikely(!pool->curr_nr)) >> > + if (unlikely(pool->curr_nr < count - allocated)) >> >> So we might be pessimistic here when some of the elements in the array >> already are not NULL so we need in fact less. Might be an issue if callers >> were relying on this for forward progress? It would be simpler to just tell >> them not to... > > Yes. I think alloc_pages_bulk always allocates from the beginning > and doesn't leave random holes? That's what a quick look at the code > suggest, unfortunately the documentation for it totally sucks. Yeah I think it's fine with alloc_pages_bulk. It would only be a concern is the bulk alloc+mempool user used up part of the allocated array, NULLing some earlier pointers but leaving later ones alone, and then attempted to refill it. >> > + * @pool: pointer to the memory pool >> > + * @elems: partially or fully populated elements array >> > + * @count: size (in entries) of @elem >> > + * @gfp_mask: GFP_* flags. %__GFP_ZERO is not supported. >> >> We should say __GFP_DIRECT_RECLAIM is mandatory... > > It's not really going to fit in there :) Maybe I should have ignored > Eric's request to mention __GFP_ZERO here and just keep everything > together. I thought it can be multiline, but if not, can refer to the notes below and explain there, yeah. >> > +repeat_alloc: >> > + /* >> > + * Try to allocate the elements using the allocation callback. If that >> > + * succeeds or we were not allowed to sleep, return now. Don't dip into >> > + * the reserved pools for !__GFP_DIRECT_RECLAIM allocations as they >> > + * aren't guaranteed to succeed and chances of getting an allocation >> > + * from the allocators using GFP_ATOMIC is higher than stealing one of >> > + * the few items from our usually small pool. >> > + */ >> >> Hm but the code doesn't do what the comment says, AFAICS? It will try >> dipping into the pool and might succeed if there are elements, only will not >> wait for them there? > Yeah, that comment is actually stale from an older version. > >> >> > + for (; i < count; i++) { >> > + if (!elems[i]) { >> > + elems[i] = pool->alloc(gfp_temp, pool->pool_data); >> > + if (unlikely(!elems[i])) >> > + goto use_pool; >> > + } >> > + } >> > + >> > + return 0; >> > + >> > +use_pool: >> >> So should we bail out here with -ENOMEM when !(gfp_mask & __GFP_DIRECT_RECLAIM)? > > No, I don't want the !__GFP_DIRECT_RECLAIM handling. It's a mess, > and while for mempool_alloc having it for compatibility might make some > sense, I'd rather avoid it for this new interface where the semantics > of failing allocations are going to be really annoying. OK. >> > + if (!mempool_alloc_from_pool(pool, elems, count, i, gfp_temp)) { >> > + gfp_temp = gfp_mask; >> > + goto repeat_alloc; >> >> Because this seems to be an infinite loop otherwise? > > You mean if someone passed in !__GFP_DIRECT_RECLAIM and got the warning > above? Yes, IFF that code makes it to production and then runs into > a low-memory situation it would. But it's an API abuse. The other > option would be to just force __GFP_DIRECT_RECLAIM. True, so let's ignore it.