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[209.85.220.65]) by mx.google.com with SMTPS id 9sor4563774ljh.27.2019.06.16.09.29.43 for (Google Transport Security); Sun, 16 Jun 2019 09:29:43 -0700 (PDT) Received-SPF: pass (google.com: domain of vdavydov.dev@gmail.com designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b="h/sR59wJ"; spf=pass (google.com: domain of vdavydov.dev@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=vdavydov.dev@gmail.com; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=ROe9l7rmNkgoXM5ZdfPpWNA4ZJ7+sjLyBm3rIg5S9KA=; b=h/sR59wJK+fRC3mRDJUs7YbyyNEHv8XpFqQto+pIOpDJRMFMGXKdTxTZAireTGxWI7 FiwYLSr2JON5mEQW2DXWE7T8sKIn1R0ReRXD5pwqAVNuRR8sz89cbggeLHCju6kvpUAD 1ja4b8jol2zMk/o5ykuyNrTYJOMC4nQs3gM6GOvIuLdZHdSfereMItNivftbGHTijBQP 0UcvIB9QCMSfYiXgJIMozMimRf/z2poqJKiEzgAm8hX4YL94zxvC5YVcufmTAcrCx7mm 109jh1L0ci4SmEfT27NtHD5LOcG1rXp2M0z8qHkzSJ1Oy6lmw/MYZAwE2vQpbf4O1+ma ziJw== X-Google-Smtp-Source: APXvYqz3gJlQxLnmSB1YMDld8wbounFH1DdB5g8n3krY1uyci2h9hWjnE9Hq3gAA/X85j5ZNacy3cg== X-Received: by 2002:a2e:93c5:: with SMTP id p5mr22338427ljh.79.1560702583227; Sun, 16 Jun 2019 09:29:43 -0700 (PDT) Received: from esperanza ([176.120.239.149]) by smtp.gmail.com with ESMTPSA id 25sm1660372ljv.40.2019.06.16.09.29.42 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Sun, 16 Jun 2019 09:29:42 -0700 (PDT) Date: Sun, 16 Jun 2019 19:29:41 +0300 From: Vladimir Davydov To: Roman Gushchin Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@fb.com, Johannes Weiner , Shakeel Butt , Waiman Long Subject: Re: [PATCH v7 10/10] mm: reparent memcg kmem_caches on cgroup removal Message-ID: <20190616162941.aqa4ae5j63nmjlp6@esperanza> References: <20190611231813.3148843-1-guro@fb.com> <20190611231813.3148843-11-guro@fb.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190611231813.3148843-11-guro@fb.com> 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, Jun 11, 2019 at 04:18:13PM -0700, Roman Gushchin wrote: > Let's reparent non-root kmem_caches on memcg offlining. This allows us > to release the memory cgroup without waiting for the last outstanding > kernel object (e.g. dentry used by another application). > > Since the parent cgroup is already charged, everything we need to do > is to splice the list of kmem_caches to the parent's kmem_caches list, > swap the memcg pointer, drop the css refcounter for each kmem_cache > and adjust the parent's css refcounter. > > Please, note that kmem_cache->memcg_params.memcg isn't a stable > pointer anymore. It's safe to read it under rcu_read_lock(), > cgroup_mutex held, or any other way that protects the memory cgroup > from being released. > > We can race with the slab allocation and deallocation paths. It's not > a big problem: parent's charge and slab global stats are always > correct, and we don't care anymore about the child usage and global > stats. The child cgroup is already offline, so we don't use or show it > anywhere. > > Local slab stats (NR_SLAB_RECLAIMABLE and NR_SLAB_UNRECLAIMABLE) > aren't used anywhere except count_shadow_nodes(). But even there it > won't break anything: after reparenting "nodes" will be 0 on child > level (because we're already reparenting shrinker lists), and on > parent level page stats always were 0, and this patch won't change > anything. > > Signed-off-by: Roman Gushchin Acked-by: Vladimir Davydov