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[209.85.220.65]) by mx.google.com with SMTPS id d9sor7848860lji.7.2019.05.28.11.33.06 for (Google Transport Security); Tue, 28 May 2019 11:33:06 -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=JdETCGK0; 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=/dxRboK00I5JVZJIcKIh8lDmjqTZ8vT2RGIZXym9hs8=; b=JdETCGK02W+TtswFGWYTMmY9WIEyBXPpCljaIU/VvB/d3DyEtFWnP0lJVxjUjx9TD+ BbFimxaiEpjpXaitfVH8KM8TBEOsn6oSsKdEWrPjq9D15Ew99jozw+GsV/lZqrVVZ0bd sGtow18Jv93Jk3c4kkSM9BZ05m3scy1imL1EdiSpaSjWhIrIPyNB9w8DdlCdVlnDOZNn KB5glui+lV+DZKpPu++CN6VKlXQmcVFXpxLJUgk52DMVAvzV1zTNcKZuZuMlzrMfr+zo qH7zlgas8ajm6z/0f37WMEh9ITFodHk5tXZpvMdRGXtAceFsYcaEo3ESqN2B34xySD+d KVXQ== X-Google-Smtp-Source: APXvYqy3s9q75FdgW1jA17eTPuwlMKdHK6SG0NcuvVUvEqKB1BuEK4FqNNQLezmX/qt3sQkeKbs49Q== X-Received: by 2002:a2e:9193:: with SMTP id f19mr24449382ljg.111.1559068386280; Tue, 28 May 2019 11:33:06 -0700 (PDT) Received: from esperanza ([176.120.239.149]) by smtp.gmail.com with ESMTPSA id a7sm171218lji.13.2019.05.28.11.33.04 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 28 May 2019 11:33:05 -0700 (PDT) Date: Tue, 28 May 2019 21:33:02 +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 , Michal Hocko , Rik van Riel , Shakeel Butt , Christoph Lameter , cgroups@vger.kernel.org, Waiman Long Subject: Re: [PATCH v5 6/7] mm: reparent slab memory on cgroup removal Message-ID: <20190528183302.zv75bsxxblc6v4dt@esperanza> References: <20190521200735.2603003-1-guro@fb.com> <20190521200735.2603003-7-guro@fb.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190521200735.2603003-7-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, May 21, 2019 at 01:07:34PM -0700, Roman Gushchin wrote: > Let's reparent memcg slab memory 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). > > So instead of reparenting all accounted slab pages, let's do reparent > a relatively small amount of kmem_caches. Reparenting is performed as > a part of the deactivation process. > > 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 and drop the css refcounter for each kmem_cache > and adjust the parent's css refcounter. Quite simple. > > Please, note that kmem_cache->memcg_params.memcg isn't a stable > pointer anymore. It's safe to read it under rcu_read_lock() or > with slab_mutex held. > > 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 > Reviewed-by: Shakeel Butt This one looks good to me. I can't see why anything could possibly go wrong after this change.