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[209.85.220.65]) by mx.google.com with SMTPS id v10sor3956014lfi.48.2019.05.28.11.00.29 for (Google Transport Security); Tue, 28 May 2019 11:00:30 -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=K5mTZO29; 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=gzRimgoeRu7R/UsHOkPXtR9NqQokG6oQDoPTeeW4GsA=; b=K5mTZO29tbBaLBfmC9xktb9UyEHFJm7cNGH2ho7TmDNYxAatoyUag706Zd7cjqjf28 KkeBW1GaNsqZpGtuXpPL2jgCnJM5DuHaiEWuudtfGOhqTqHMJOGDCHv8YAGmcWlXiSLK tvB79wzMLr5Um6QS7j3cKNsAv1752T6NIpZ/9dqKNuDh+uFqgoopmTVuvev/Ic1UEPV9 POninSj+/FBXrDQrPHxHzYlplgfdBdt11aQdVLcmU7bI3aGISf73jtSTKnsqq7hOE1Hl V+x+dWvcxXzA/c6PZ2CFDN+iGZBodzbs4Zs7PsfeskXJix3j7cStbEXLgSLKM7CJ7KPj kKnQ== X-Google-Smtp-Source: APXvYqza2BE+UrIAhAKBPOR5jKGph27QtzFQbF50zdcH09u6RqUIDrc1Df0ox4XY650tVc7LO0usqA== X-Received: by 2002:ac2:5285:: with SMTP id q5mr8975099lfm.146.1559066429696; Tue, 28 May 2019 11:00:29 -0700 (PDT) Received: from esperanza ([176.120.239.149]) by smtp.gmail.com with ESMTPSA id e19sm3048133ljj.62.2019.05.28.11.00.28 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 28 May 2019 11:00:29 -0700 (PDT) Date: Tue, 28 May 2019 21:00:26 +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 5/7] mm: rework non-root kmem_cache lifecycle management Message-ID: <20190528180026.zb6yaxdeapwx5r3v@esperanza> References: <20190521200735.2603003-1-guro@fb.com> <20190521200735.2603003-6-guro@fb.com> <20190528170828.zrkvcdsj3d3jzzzo@esperanza> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190528170828.zrkvcdsj3d3jzzzo@esperanza> 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 28, 2019 at 08:08:28PM +0300, Vladimir Davydov wrote: > Hello Roman, > > On Tue, May 21, 2019 at 01:07:33PM -0700, Roman Gushchin wrote: > > This commit makes several important changes in the lifecycle > > of a non-root kmem_cache, which also affect the lifecycle > > of a memory cgroup. > > > > Currently each charged slab page has a page->mem_cgroup pointer > > to the memory cgroup and holds a reference to it. > > Kmem_caches are held by the memcg and are released with it. > > It means that none of kmem_caches are released unless at least one > > reference to the memcg exists, which is not optimal. > > > > So the current scheme can be illustrated as: > > page->mem_cgroup->kmem_cache. > > > > To implement the slab memory reparenting we need to invert the scheme > > into: page->kmem_cache->mem_cgroup. > > > > Let's make every page to hold a reference to the kmem_cache (we > > already have a stable pointer), and make kmem_caches to hold a single > > reference to the memory cgroup. > > Is there any reason why we can't reference both mem cgroup and kmem > cache per each charged kmem page? I mean, > > page->mem_cgroup references mem_cgroup > page->kmem_cache references kmem_cache > mem_cgroup references kmem_cache while it's online > > TBO it seems to me that not taking a reference to mem cgroup per charged > kmem page makes the code look less straightforward, e.g. as you > mentioned in the commit log, we have to use mod_lruvec_state() for memcg > pages and mod_lruvec_page_state() for root pages. I think I completely missed the point here. In the following patch you move kmem caches from a child to the parent cgroup on offline (aka reparent them). That's why you can't maintain page->mem_cgroup. Sorry for misunderstanding.