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[108.27.252.85]) by smtp.gmail.com with ESMTPSA id t7sm1574736qkm.136.2020.02.06.07.46.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 06 Feb 2020 07:46:25 -0800 (PST) Date: Thu, 6 Feb 2020 10:46:24 -0500 From: Johannes Weiner To: Dan Schatzberg Cc: Jens Axboe , Tejun Heo , Li Zefan , Michal Hocko , Vladimir Davydov , Andrew Morton , Hugh Dickins , "open list:BLOCK LAYER" , open list , "open list:CONTROL GROUP (CGROUP)" , "open list:CONTROL GROUP - MEMORY RESOURCE CONTROLLER (MEMCG)" Subject: Re: [PATCH 2/2] loop: charge i/o per cgroup Message-ID: <20200206154624.GB24735@cmpxchg.org> References: <20200205223348.880610-1-dschatzberg@fb.com> <20200205223348.880610-3-dschatzberg@fb.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200205223348.880610-3-dschatzberg@fb.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello Dan, On Wed, Feb 05, 2020 at 02:33:48PM -0800, Dan Schatzberg wrote: > @@ -1925,14 +1990,13 @@ static blk_status_t loop_queue_rq(struct blk_mq_hw_ctx *hctx, > } > > /* always use the first bio's css */ > + cmd->blk_css = NULL; > #ifdef CONFIG_BLK_CGROUP > - if (cmd->use_aio && rq->bio && rq->bio->bi_blkg) { > - cmd->css = &bio_blkcg(rq->bio)->css; > - css_get(cmd->css); > - } else > + if (rq->bio && rq->bio->bi_blkg) > + cmd->blk_css = &bio_blkcg(rq->bio)->css; > #endif > - cmd->css = NULL; > - kthread_queue_work(&lo->worker, &cmd->work); > + > + loop_queue_work(lo, cmd); > > return BLK_STS_OK; > } > @@ -1942,6 +2006,9 @@ static void loop_handle_cmd(struct loop_cmd *cmd) > struct request *rq = blk_mq_rq_from_pdu(cmd); > const bool write = op_is_write(req_op(rq)); > struct loop_device *lo = rq->q->queuedata; > +#ifdef CONFIG_MEMCG > + struct cgroup_subsys_state *mem_css; > +#endif > int ret = 0; > > if (write && (lo->lo_flags & LO_FLAGS_READ_ONLY)) { > @@ -1949,8 +2016,24 @@ static void loop_handle_cmd(struct loop_cmd *cmd) > goto failed; > } > > + if (cmd->blk_css) { > +#ifdef CONFIG_MEMCG > + mem_css = cgroup_get_e_css(cmd->blk_css->cgroup, > + &memory_cgrp_subsys); > + memalloc_use_memcg(mem_cgroup_from_css(mem_css)); > +#endif > + kthread_associate_blkcg(cmd->blk_css); > + } > + > ret = do_req_filebacked(lo, rq); > - failed: > + > + if (cmd->blk_css) { > + kthread_associate_blkcg(NULL); > +#ifdef CONFIG_MEMCG > + memalloc_unuse_memcg(); > +#endif cgroup_get_e_css() acquires a reference, it looks like you're missing a css_put() here. I also wonder why you look up blk_css and mem_css in separate places. Since you already renamed cmd->css to cmd->blk_css, can you also add cmd->mem_css and pair up their lookup and refcounting? This should make loop_handle_cmd() a bit more straight-forward: if (cmd->blk_css) kthread_associate_blkcg(cmd->blk_css); if (cmd->mem_css) memalloc_use_memcg(mem_cgroup_from_css(mem_css)); ret = do_req_filebacked(lo, rq); memalloc_unuse_memcg(); kthread_associate_blkcg(NULL); All these functions have dummy implementations for !CONFIG_BLK_CGROUP, !CONFIG_MEMCG etc., so it shouldn't require any additional ifdefs.