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DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1761669824; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=kSNkRhOJhrPtd4Js2oBI0wr+MEc/sKamTAOCSggnfZY=; b=C9XyJNAQbLdaKmF6tYaMQJgBraElANn8UZADDHK2VL+pgdD76IApnxrZRyQYAaT6rFTarg tYoLJbg0VWb22xMZArp0wH2Ft+STPLO0i2hYX2TtGMWEJM/N10vBHM5tQfD5nGj0ItMa51 otG8PaOIqzlX0JNrVvhEtQ7NWlSELLQ= From: Roman Gushchin To: bot+bpf-ci@kernel.org Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org, ast@kernel.org, surenb@google.com, mhocko@kernel.org, shakeel.butt@linux.dev, hannes@cmpxchg.org, andrii@kernel.org, inwardvessel@gmail.com, linux-mm@kvack.org, cgroups@vger.kernel.org, bpf@vger.kernel.org, martin.lau@kernel.org, song@kernel.org, memxor@gmail.com, tj@kernel.org, daniel@iogearbox.net, eddyz87@gmail.com, yonghong.song@linux.dev, clm@meta.com, ihor.solodrai@linux.dev Subject: Re: [PATCH v2 13/23] mm: introduce bpf_out_of_memory() BPF kfunc In-Reply-To: <2b04ce21d82f2118c291c49ace22d685bcbbd45d203b2f676556d3e5a90eebd1@mail.kernel.org> (bot's message of "Mon, 27 Oct 2025 23:57:21 +0000 (UTC)") References: <20251027232206.473085-3-roman.gushchin@linux.dev> <2b04ce21d82f2118c291c49ace22d685bcbbd45d203b2f676556d3e5a90eebd1@mail.kernel.org> Date: Tue, 28 Oct 2025 09:43:36 -0700 Message-ID: <87cy673rk7.fsf@linux.dev> MIME-Version: 1.0 Content-Type: text/plain X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 2C45CC0006 X-Stat-Signature: 9ifkk5wjhs4cm8eba8ykwepgpm4d1xep X-HE-Tag: 1761669826-340304 X-HE-Meta: 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 43/VB6md QW235HYrO7INFO1O3bTrUD6ufE06zzqy3d26EywT446YhNFqWV0wsrUQDzmdbrHq3zRJcN4CbEXqyBWG3fGwt10W+EJpPPJs46L4EVGKQcgzbrgqyhDBa4UBbYoNZOpqslq42lR2sXwDWKaCY9OVzDBtrKN5/uv1Tnd6Tuiy89VrOk06M/1BnmTbXMBZLbHA8TeqXhUrmKuwSlHlHyMQ4zi2RQbatR2OH9iv70i9wJcgHbeaz/RENtWYOGj3UPYV8J0JdIoAc7yl45HMAdjHvyBdzvQ== 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: bot+bpf-ci@kernel.org writes: > ``` > commit bce57b9b96e05731a14c7e10a364fdd9b733cda2 > Author: Roman Gushchin > > mm: introduce bpf_out_of_memory() BPF kfunc > > This patch introduces bpf_out_of_memory() BPF kfunc to allow BPF programs > to declare OOM events and trigger the kernel OOM handling mechanism. The > function accepts a nullable memcg pointer for system-wide or memcg-scoped > OOMs. > >> diff --git a/include/linux/oom.h b/include/linux/oom.h >> index 721087952..3cbdcd013 100644 >> --- a/include/linux/oom.h >> +++ b/include/linux/oom.h >> @@ -21,6 +21,11 @@ enum oom_constraint { >> CONSTRAINT_MEMCG, >> }; >> >> +enum bpf_oom_flags { >> + BPF_OOM_FLAGS_WAIT_ON_OOM_LOCK = 1 << 0, >> + BPF_OOM_FLAGS_LAST = 1 << 1, >> +}; >> + >> /* >> * Details of the page allocation that triggered the oom killer that are used to >> * determine what should be killed. >> diff --git a/mm/oom_kill.c b/mm/oom_kill.c >> index 3c86cd755..d7fca4bf5 100644 >> --- a/mm/oom_kill.c >> +++ b/mm/oom_kill.c > > [ ... ] > >> +/** >> + * bpf_out_of_memory - declare Out Of Memory state and invoke OOM killer >> + * @memcg__nullable: memcg or NULL for system-wide OOMs >> + * @order: order of page which wasn't allocated >> + * @flags: flags >> + * @constraint_text__nullable: custom constraint description for the OOM report >> + * >> + * Declares the Out Of Memory state and invokes the OOM killer. >> + * >> + * OOM handlers are synchronized using the oom_lock mutex. If wait_on_oom_lock >> + * is true, the function will wait on it. Otherwise it bails out with -EBUSY >> + * if oom_lock is contended. >> + * >> + * Generally it's advised to pass wait_on_oom_lock=false for global OOMs >> + * and wait_on_oom_lock=true for memcg-scoped OOMs. >> + * >> + * Returns 1 if the forward progress was achieved and some memory was freed. >> + * Returns a negative value if an error occurred. >> + */ >> +__bpf_kfunc int bpf_out_of_memory(struct mem_cgroup *memcg__nullable, >> + int order, u64 flags) >> +{ >> + struct oom_control oc = { >> + .memcg = memcg__nullable, >> + .order = order, >> + }; > > Can bpf_out_of_memory() work correctly for system-wide OOMs with > uninitialized gfp_mask? > > Looking at out_of_memory(): > > if (!(oc->gfp_mask & __GFP_FS) && !is_memcg_oom(oc)) > return true; > > With gfp_mask=0 and memcg=NULL (system-wide OOM), this evaluates to: > !(0 & __GFP_FS) && !false = true, causing an early return without > invoking the OOM killer. The comment in out_of_memory() explains this > check is about allocation context: "The OOM killer does not compensate > for IO-less reclaim." > > All other callers of out_of_memory() initialize gfp_mask: > - mm/page_alloc.c: .gfp_mask = gfp_mask > - mm/memcontrol.c: .gfp_mask = gfp_mask > > For memcg OOMs, the code works because is_memcg_oom(oc) is true, > bypassing the check. But for system-wide OOMs (NULL memcg), won't this > cause the function to return immediately without killing any process? This is a good catch! It must be .gfp_mask = GFP_KERNEL. Fixed. Thanks!