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[70.52.229.124]) by smtp.gmail.com with ESMTPSA id l5-20020a05620a210500b0074cf009f443sm2553280qkl.85.2023.04.18.11.46.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 18 Apr 2023 11:46:17 -0700 (PDT) Date: Tue, 18 Apr 2023 14:46:15 -0400 From: Peter Xu To: Suren Baghdasaryan Cc: Matthew Wilcox , akpm@linux-foundation.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-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 5098940022 X-Rspam-User: X-Stat-Signature: r3mr1aidikta979xo64nz5fs8bgy9nrb X-HE-Tag: 1681843580-944745 X-HE-Meta: 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 sxaZx8WO vbOpUtFQJHDy5Mv+79HA1H7h2/SNnIF3fZWTv59cC7m+d9YY0GKCWWMWqy7uSYgpj0qMdFztOglpJ7oXYCwknlvSA1XJjRln8DWTtijC1vywP7GRZlFiXUcVIsHIVjnBtunoCnvNPzxiRtipbAl8WMIOcFJlB42T8V7ufRswKw8uLcJ9a0iPrCzz8mzI0wkU3Lxj/vHAfOlh5Kospwy4KgPQwsSjDSc/+kJj+4XYwgR+1ijmbrIL85PDNUmpeSvYdDed5+fWm39l0w2h1Hio19HIB2GPxnE2mijO3Clp1lm7NPRvp+kYiwbMXUBZ2TTkhkPaVdgJylBrbQagnEtAyjJRaEiosUMDnoewDAC2o1B2RDpWOaZ6SI+tdlg3DuWAo8/vVNh/nEry2DkTo/Ar8oMFWGg== 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: On Tue, Apr 18, 2023 at 09:45:52AM -0700, Suren Baghdasaryan wrote: > On Tue, Apr 18, 2023 at 8:48 AM Peter Xu wrote: > > > > On Tue, Apr 18, 2023 at 04:32:27PM +0100, Matthew Wilcox wrote: > > > ... when we called clone()? A thread by definition has a reference to > > > its own mm. > > > > Ah yes.. thanks! > > re: 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. > > We recycle mm after all refcounts are dropped in the exit path: > do_exit > exit_mm > mmput(if !mm->mm_users) > mmdrop(if !mm->mm_count) > free_mm I assume Matthew means when the task_struct is created with part of kernel_clone(). copy_mm() has: if (clone_flags & CLONE_VM) { mmget(oldmm); mm = oldmm; } else { mm = dup_mm(tsk, current->mm); if (!mm) return -ENOMEM; } If CLONE_VM, we'll mmget() on the existing mm. If !CLONE_VM, we'll just create a new one with reference held. For the latter, I think that hides in mm_init() where it'll just set it to 1: atomic_set(&mm->mm_users, 1); With mm_users>0, do_exit() will leave the mm_struct* alone since mmput() will still be called but not the final step on mmdrop(). Thanks, -- Peter Xu