From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 62399C77B75 for ; Tue, 18 Apr 2023 18:47:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232575AbjDRSrH (ORCPT ); Tue, 18 Apr 2023 14:47:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38372 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231168AbjDRSrD (ORCPT ); Tue, 18 Apr 2023 14:47:03 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 020FF2694 for ; Tue, 18 Apr 2023 11:46:20 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1681843580; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=BB7vJoU3HrrLNxTi8Xk72x9Aag8/v7/whz+Iy4S1B8Q=; b=LXhFFRg/NVCzPkYdOh1yK9Ophktn4fgdMyxYo0QnFRerKYP31w83TpZnNx+yW4fgOo5DK1 IfB1O98ECxqAqBDwig6sX7o6KRaHu+cntczFftZS5+oIGpZRiBfTXzTsbWEHktipd5LkY0 zhqL33YXNCeWUk4lXEkcpl+wbDS34Zw= Received: from mail-qt1-f199.google.com (mail-qt1-f199.google.com [209.85.160.199]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-543-LtQTkdBIO7C4mUIZ7IzFuA-1; Tue, 18 Apr 2023 14:46:18 -0400 X-MC-Unique: LtQTkdBIO7C4mUIZ7IzFuA-1 Received: by mail-qt1-f199.google.com with SMTP id d75a77b69052e-3ecd50d9db9so4601141cf.0 for ; Tue, 18 Apr 2023 11:46:18 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1681843578; x=1684435578; h=in-reply-to:content-transfer-encoding:content-disposition :mime-version:references:message-id:subject:cc:to:from:date :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=BB7vJoU3HrrLNxTi8Xk72x9Aag8/v7/whz+Iy4S1B8Q=; b=PQk2G6Fu0nVKZgB3rUnzVMxmhAfdUJ5WOyohS+XWQaWPYe/Y8rUivhxnhwMpP7K9QJ 0U0D89DsPBB9Stli9QtkyYyKHVNz95BBATRSMJlUm7R77AQrRcGY4kidplj+RlAv0YaE xUaM0B04a9lX7OruFJ7yWzFMf5g3C49CW1cJsCM7qCtaWIKN96gTEMNfyXg+hx66r12h fkjwAb6VTo/PIfciygDWhzQZD1FZHE5IsvjtCx0ZQnngpDUGW9FJ3aEymzQ7o/KZwb4U CoEWyZh+nA2KgItxbB7WAfRtUkIeCDHk7AgplafWlmOkLEzmkN9tm/6RH75GbeBkTzk8 Ws3w== X-Gm-Message-State: AAQBX9ciSlWmlK3NgtZ6SVcoej+OCC19CPckceE/a8QATm/jFyX7iltW nXcME7BMoKHXuZM1W4+DRtL+NjCwPPpyC6dfTwZ094qCMGVpTGzVrEp43LXjqntSVdkp/uWSuyo XVRuFMc85DsoEnhTFWUXbXCpt X-Received: by 2002:a05:622a:1352:b0:3ef:37fa:e1d6 with SMTP id w18-20020a05622a135200b003ef37fae1d6mr7109281qtk.2.1681843578060; Tue, 18 Apr 2023 11:46:18 -0700 (PDT) X-Google-Smtp-Source: AKy350aaYkIPSXh56iejgXsondxtvJiaCp+DeLUdNdH+yalmk8s8oiHwbrbN5wEHL54x9K9oqF0MMA== X-Received: by 2002:a05:622a:1352:b0:3ef:37fa:e1d6 with SMTP id w18-20020a05622a135200b003ef37fae1d6mr7109253qtk.2.1681843577799; Tue, 18 Apr 2023 11:46:17 -0700 (PDT) Received: from x1n (bras-base-aurron9127w-grc-40-70-52-229-124.dsl.bell.ca. [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 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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