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Fri, 21 Mar 2025 11:26:20 +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 5bo4EtxM3WdUQQAAD6G6ig (envelope-from ); Fri, 21 Mar 2025 11:26:20 +0000 Date: Fri, 21 Mar 2025 11:26:18 +0000 From: Pedro Falcato To: Lorenzo Stoakes Cc: Andrew Morton , Vlastimil Babka , Jann Horn , "Liam R . Howlett" , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 6.15] mm/vma: add give_up_on_oom option on modify/merge, use in uffd release Message-ID: <233o4lohzhriye27szk6mucduneuvosmnp6pmnjepz3enxjgtt@id6kwhjgysbj> References: <20250321100937.46634-1-lorenzo.stoakes@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250321100937.46634-1-lorenzo.stoakes@oracle.com> X-Rspamd-Server: rspam01 X-Stat-Signature: jabqwqwh1s19rxmtq4o4hmao1ihyr7kb X-Rspam-User: X-Rspamd-Queue-Id: C7B78A001A X-HE-Tag: 1742556382-796400 X-HE-Meta: U2FsdGVkX1//2Wp4cZcOv8VyyO+moSYDwZl3dbf0HB4qyhPwQiGveyRwNbPV+N0tbZSfWrqng6hAufpDx96JCQkCySM1F9roNLsc0TAhQ0QR9rrmUSt1HxozUTpk6+6r+OYhJnyyeTn4X8kc/U1orRN9AM8ukLl+QYBF4d3RIEUCoxOL1lC2ZSAzJIcxa2s+ZlU5e80Se/Linu6qnGK1pNfiQy3T8VIZJqD8/eyxoW/sIW4Nxy2f3ytLEzQncck7SiUixwXVB5uuT3pPQvSLaw2mcLjtFrwlnKjHRR9gBBavU/Hb+0teSHyHuWC5wPMAEGiwdM1YMb4qJI7HLttl4tDr+eYmdyRrPW1rI7TIAmt43lSQE29ytSiPMdJcVOmSUU4hhLL5Kj/JJ08GWkI1MK6gnnlYeDegAAQm0KSWRuIX/bJCsGs2KOkvN5EjkCtDY4RvPxhkcV61qpyZ2CJOvhKVpXLmEac1wqxif1/kENshPWpY1WSw9u8JLoohN6h+gArQSX8QW6zwOYQpDO2LtYnucaGJ44cMvzgG+pbvG5GHtgoCqFpf2mWCVoV5Wz8xk5gUINv3LhtYdCNwpEQLhZZa6tk4V6BC/lF+j9vTfPHQ/PxaAejLnI7IfTkDRl/hIaJbSqwInHkHmSYRDBLDYLN/irwN99qDbBvse25IybAopcQSjWw8V3HtcpXx25oHinQWpEXeHploboZn9qDn8BpyGnCEGboJZ/84e5m6lxjTfeCBKm4ii8Nf53939hM1x98CDm7TVa5NAtYeV03H+0pUGZiUPhTO4QkSlwb1XmCK7DK4juGFfPKJ9k1oPuez2nAvoAU76JKVkwlJfCaKLzh9+m3Qc/G7W6qi0wAkGAz/iNSjuGyJCmUmZrRY6AHJDF5VINl2y6bJqfvMOHaGe4B7+L/FpOi4qDyp8t99mgliHRgHvXkI2tpoiLYZeacTNYCIQjYeHnlOpfGgLkb QUsWhtQ+ 8lwIUqxFGRyQa7yr0iLFmmiShdKpSgDeiim9Gk9hPTNhi/r5Zieedou6Jzui1U/H6J9iEMzRglulKOz+uEnpivyel51jrg8b/AgyEhS7Ci/Y+5OEJRqcdosrziVU81rP4Ue/DiJX6B4um2FEbC+F+Gj9affaE418Wrtg4kKIQ48PYYy9MWLzSBTQd3TpBbXTi9i5rN3/6XGbHhoglh5MiKgw4XxmW5oH0j6ibgBEvq1cAjUz8ZvwdFy+ONq8nnPycmJolMVJOjmKKXIRVRa8DjsDNnpqjfxp51OQG8f9BQj/Zl2zCVtIGpC+8+tmGEePnGD6BA5BTuVZQBftzNndXq0Cv3IS47Bj+m10x X-Bogosity: Ham, tests=bogofilter, spamicity=0.020537, 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 Fri, Mar 21, 2025 at 10:09:37AM +0000, Lorenzo Stoakes wrote: > Currently, if a VMA merge fails due to an OOM condition arising on commit > merge or a failure to duplicate anon_vma's, we report this so the caller > can handle it. > > However there are cases where the caller is only ostensibly trying a > merge, and doesn't mind if it fails due to this condition. > Ok, so here's my problem with your idea: I don't think merge should be exposed to vma_modify() callers. Right now (at least AIUI), you want to modify a given VMA, you call vma_modify(), and it gives you a vma you can straight up modify without any problems. Essentially breaks down any VMAs necessary. This feels contractually simple and easy to use, and I don't think leaking details about merging is the correct approach here. > Since we do not want to introduce an implicit assumption that we only > actually modify VMAs after OOM conditions might arise, add a 'give up on > oom' option and make an explicit contract that, should this flag be set, we > absolutely will not modify any VMAs should OOM arise and just bail out. > Thus, to me the most natural solution is still mine. Do you think it places too many constraints on vma_modify()? vma_modify() on a single VMA, without splitting, Just Working(tm) is a sensible expectation (and vma_merge being fully best-effort). Things like mprotect() failing due to OOM are also pretty disastrous, so if we could limit that it'd be great. In any case, your solution looks palatable to me, but I want to make sure we're not making this excessively complicated. -- Pedro