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[70.52.229.124]) by smtp.gmail.com with ESMTPSA id l5-20020a05620a210500b0074cf009f443sm2422417qkl.85.2023.04.18.08.19.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 18 Apr 2023 08:19:42 -0700 (PDT) Date: Tue, 18 Apr 2023 11:19:40 -0400 From: Peter Xu To: Suren Baghdasaryan Cc: akpm@linux-foundation.org, willy@infradead.org, hannes@cmpxchg.org, mhocko@suse.com, josef@toxicpanda.com, jack@suse.cz, ldufour@linux.ibm.com, laurent.dufour@fr.ibm.com, michel@lespinasse.org, liam.howlett@oracle.com, jglisse@google.com, vbabka@suse.cz, minchan@google.com, dave@stgolabs.net, punit.agrawal@bytedance.com, lstoakes@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@android.com Subject: Re: [PATCH v2 1/1] mm: do not increment pgfault stats when page fault handler retries Message-ID: References: <20230415000818.1955007-1-surenb@google.com> MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam03 X-Stat-Signature: kd44rnqhej5h1358x7bj3odx89tsacwk X-Rspamd-Queue-Id: 628381C001C X-HE-Tag: 1681831188-520584 X-HE-Meta: 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 MIgpdcK5 7sWrNZ3MNXiaxisodBMglyRaDJ9kraQTjLj1R9Z6V6gtJTGk1UBmSV+r70QWn+bXCLMXKbwUJON5FdquWhI141I/h64CBYQrJHWUcUzesWIjQ08H80DPxZAouNVbDhM94pf+ueJURgI0TWdbKQbbhYdwZIWYKzW4kRxqVJA6mSJKlyyJTHxMrIdUP3v7oxmwbM6RvAmuUblpktLvgMuDfEf8LEharzhlp1rQ3WMNemRexKZmqY8TGmB2/iQTjnsUxNOVxS29tuCJIz4xzFAsDD/pOPZbKAyRjX5F5Fg4+a8S/ilLketTOhl5HRIaQByGtGAh4KRbH8RqWQQ7ieB6FdZT6bi3ys6pSesCIlIAIPm1j9lnPBn/nRoM04WJuSnjesHJ1gyzAaqEpfo9OqC89RUFvXw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000001, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Apr 17, 2023 at 03:47:57PM -0700, Suren Baghdasaryan wrote: > On Mon, Apr 17, 2023 at 2:26 PM Peter Xu wrote: > > > > On Fri, Apr 14, 2023 at 05:08:18PM -0700, Suren Baghdasaryan wrote: > > > @@ -5223,8 +5230,8 @@ vm_fault_t handle_mm_fault(struct vm_area_struct *vma, unsigned long address, > > > if (task_in_memcg_oom(current) && !(ret & VM_FAULT_OOM)) > > > mem_cgroup_oom_synchronize(false); > > > } > > > - > > > - mm_account_fault(regs, address, flags, ret); > > > +out: > > > + mm_account_fault(mm, regs, address, flags, ret); > > > > Ah, one more question.. can this cached mm race with a destroying mm (just > > like the vma race we wanted to avoid)? Still a question only applies to > > COMPLETE case when mmap read lock can be released. Thanks, > > I believe that is impossible because whoever is calling the page fault > handler has stabilized the mm by getting a refcount. Do you have a hint on where that refcount is taken? Btw, it's definitely not a question sololy for this patch but a more common question to the page fault path. It's just that when I wanted to look for any refcount boost (which I also expect to have somewhere) I didn't really see that in current path (e.g. do_user_addr_fault() for x86_64). I also had a quick look on do_exit() but I also didn't see where do we e.g. wait for all the threads to stop before recycles a mm. I had a feeling that I must have missed something, but just want to make sure it's the case. -- Peter Xu