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[195.250.132.146]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-429dc1f9cdbsm4467712f8f.34.2025.11.04.04.50.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 04 Nov 2025 04:50:05 -0800 (PST) Date: Tue, 4 Nov 2025 13:50:04 +0100 From: Michal Hocko To: Vlastimil Babka Cc: Matthew Wilcox , Shakeel Butt , libaokun@huaweicloud.com, linux-mm@kvack.org, akpm@linux-foundation.org, surenb@google.com, jackmanb@google.com, hannes@cmpxchg.org, ziy@nvidia.com, jack@suse.cz, yi.zhang@huawei.com, yangerkun@huawei.com, libaokun1@huawei.com Subject: Re: [PATCH RFC] mm: allow __GFP_NOFAIL allocation up to BLK_MAX_BLOCK_SIZE to support LBS Message-ID: References: <9d5790f0-4a07-4cca-9f94-de101084a7e6@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: B86B280004 X-Stat-Signature: ymkk84h5nq8drdrwh6fp9tmd3ppuqbmp X-HE-Tag: 1762260607-705068 X-HE-Meta: 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 /i1PSbGP fgAlUBH5qffyuWqIo1BcZVKmAq0f1VpG4yvQwlAAtt7UWOJCCKsumcOjDGBqj0O3DF9U77yXZqIuTUicMPz0US07NV4dt6tLPdyF6oaxcAriZVx/upw+bZMAwclqXOLkHtSM4cBDL5hkIf92ViV98eqbUNzvJivFnJOvL8IksDYTZLjmef4iQo4mak1KK+ana9xThNToWL+JGkhHjnU9VbFrxf60grUaQlymQ2h5vVyBIdOiSXwEjrwfY6wA1Ytu5EbuZvtr9JX8uVW5l0jBRxoc076mtKiE1t17PONQwrOmHqDA4aa3Jb5ByVHDTH/5Clohsr5SLTPCLqUcTvUlxnl4CnD60EbxMSg6CkKZlJ+VxgJsJmgGMJDnN4F1oIuqFxY4KRRL+VLN88T+7f5JfXtaAVQ== 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 Tue 04-11-25 13:32:52, Vlastimil Babka wrote: > On 11/4/25 11:31 AM, Michal Hocko wrote: > > On Mon 03-11-25 10:25:40, Michal Hocko wrote: > >> On Mon 03-11-25 10:01:54, Vlastimil Babka wrote: > >>> Maybe we could keep the warning for >=PMD_ORDER as that would still mean > >>> someone made an error? > >> > >> I am not sure TBH. For those large requests (anything that is costly > >> order) it is essentially a loop around allocator inside the allocator. > >> I would be really much more worried about order-3 which still triggers > >> the oom killer and could kill half of the system without much progress. > >> For oder-2 you at least have task_struct which spans 2 pages but I do > >> not think we have any guaranteed order-3 page for each task to guarantee > >> anything when killing those. > > > > Essentially something like this > > diff --git a/mm/oom_kill.c b/mm/oom_kill.c > > index 25923cfec9c6..2df477d97cee 100644 > > --- a/mm/oom_kill.c > > +++ b/mm/oom_kill.c > > @@ -1142,6 +1142,14 @@ bool out_of_memory(struct oom_control *oc) > > if (!(oc->gfp_mask & __GFP_FS) && !is_memcg_oom(oc)) > > return true; > > > > + /* > > + * unlike for other !costly requests killing a task is not > > + * really guaranteed to free any order-3 pages. Warn about > > + * that to see whether that happens often enough to special > > + * case. > > + */ > > + WARN_ON(oc->order == 3 && (oc->gfp_mask & __GFP_NOFAIL)); > > OK, it might not create an order-3 page immediately. But I'd expect it > allows compaction to make progress thanks to making more free memory > available? We do retry reclaim/compaction after OOM killing one process, > and don't just kill until we succeed allocating, right? Yes we do go through the reclaim/compaction cycle. Do you think this warning is overzealous? Th idea is that a flood of OOMs could be easier to pin point with this in place. It doesn't have to be full WARN_ON, maybe pr_warn would be sufficient as the backtrace is usually printed in the oom report. -- Michal Hocko SUSE Labs