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Fri, 18 Sep 2026 10:59:36 -0700 (PDT) Content-Type: text/plain; charset=UTF-8 Date: Fri, 18 Sep 2026 17:59:35 +0000 Message-Id: Cc: "Emil Tsalapatis" , "Daniel Borkmann" , "Andrii Nakryiko" , "Eduard Zingerman" , "Kumar Kartikeya Dwivedi" , "Martin KaFai Lau" , "Song Liu" , "Yonghong Song" , "Jiri Olsa" , "Ihor Solodrai" , "Shuah Khan" , , Subject: Re: [PATCH bpf-next v8 1/3] bpf: arena: allocate the fault-in page outside the lock From: "Alexei Starovoitov" To: "Jiayuan Chen" , In-Reply-To: <20260918084123.39477-2-jiayuan.chen@linux.dev> References: <20260918084123.39477-1-jiayuan.chen@linux.dev> <20260918084123.39477-2-jiayuan.chen@linux.dev> X-Mailer: mkdraft (claude review draft; edit before sending) Content-Transfer-Encoding: 8bit Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Fri, Sep 18, 2026 at 04:40 PM Jiayuan Chen wrote: > @@ -489,59 +490,108 @@ static vm_fault_t arena_vm_fault(struct vm_fault *vmf) > kbase = bpf_arena_get_kern_vm_start(arena); > kaddr = kbase + (u32)(vmf->address); > > - if (raw_res_spin_lock_irqsave(&arena->spinlock, flags)) > + page = vmalloc_to_page((void *)kaddr); > + if (!page && !(arena->map.map_flags & BPF_F_SEGV_ON_FAULT)) { > + /* > + * Preallocate outside the lock so the allocation can sleep and > + * reclaim, which the non-blocking allocator under > + * arena->spinlock cannot. __GFP_RETRY_MAYFAIL: reclaim, but > + * never OOM-kill in the map's memcg, which need not be the > + * faulting task's. On failure, fallthrough: the locked > + * recheck below picks up a page a concurrent allocator may > + * have installed meanwhile, and otherwise the non-blocking > + * fallback fails and we return VM_FAULT_SIGBUS. Not > + * VM_FAULT_OOM: nothing ran the OOM killer, an d the fault path > + * would just retry it forever. > + */ I asked for one line comment. This block and the one in !new_page branch below repeat the commit log. Trim both to a sentence or two. pw-bot: cr