Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760261AbZDQJp2 (ORCPT ); Fri, 17 Apr 2009 05:45:28 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758687AbZDQJpN (ORCPT ); Fri, 17 Apr 2009 05:45:13 -0400 Received: from mail-bw0-f163.google.com ([209.85.218.163]:36722 "EHLO mail-bw0-f163.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757018AbZDQJpL (ORCPT ); Fri, 17 Apr 2009 05:45:11 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=date:from:to:cc:subject:message-id:mail-followup-to:references :mime-version:content-type:content-disposition:in-reply-to :user-agent; b=voTk043K6GYaGTOBsPOKLw8pkmMyjoyccy2OTLqlWTaoMOLgRMjDj6yAUktVAoff8L Hh5608kjKhsa0lEQWy8PA/Jfl4IFbMMYj3jMx3k7p4W1Ssis83hQDapQwrnVQs5L6NVe r3T17sdk0Nnh++w8InrbyR2aM2fSFTU91NHqQ= Date: Fri, 17 Apr 2009 11:37:44 +0200 From: Andrea Righi To: Andrew Morton Cc: menage@google.com, balbir@linux.vnet.ibm.com, guijianfeng@cn.fujitsu.com, kamezawa.hiroyu@jp.fujitsu.com, agk@sourceware.org, axboe@kernel.dk, baramsori72@gmail.com, chlunde@ping.uio.no, dave@linux.vnet.ibm.com, dpshah@google.com, eric.rannaud@gmail.com, fernando@oss.ntt.co.jp, taka@valinux.co.jp, lizf@cn.fujitsu.com, matt@bluehost.com, dradford@bluehost.com, ngupta@google.com, randy.dunlap@oracle.com, roberto@unbit.it, ryov@valinux.co.jp, s-uchida@ap.jp.nec.com, subrata@linux.vnet.ibm.com, yoshikawa.takuya@oss.ntt.co.jp, containers@lists.linux-foundation.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 0/9] cgroup: io-throttle controller (v13) Message-ID: <20090417093744.GA8689@linux> Mail-Followup-To: Andrew Morton , menage@google.com, balbir@linux.vnet.ibm.com, guijianfeng@cn.fujitsu.com, kamezawa.hiroyu@jp.fujitsu.com, agk@sourceware.org, axboe@kernel.dk, baramsori72@gmail.com, chlunde@ping.uio.no, dave@linux.vnet.ibm.com, dpshah@google.com, eric.rannaud@gmail.com, fernando@oss.ntt.co.jp, taka@valinux.co.jp, lizf@cn.fujitsu.com, matt@bluehost.com, dradford@bluehost.com, ngupta@google.com, randy.dunlap@oracle.com, roberto@unbit.it, ryov@valinux.co.jp, s-uchida@ap.jp.nec.com, subrata@linux.vnet.ibm.com, yoshikawa.takuya@oss.ntt.co.jp, containers@lists.linux-foundation.org, linux-kernel@vger.kernel.org References: <1239740480-28125-1-git-send-email-righi.andrea@gmail.com> <20090416152433.aaaba300.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090416152433.aaaba300.akpm@linux-foundation.org> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4491 Lines: 126 On Thu, Apr 16, 2009 at 03:24:33PM -0700, Andrew Morton wrote: > On Tue, 14 Apr 2009 22:21:11 +0200 > Andrea Righi wrote: > > > Objective > > ~~~~~~~~~ > > The objective of the io-throttle controller is to improve IO performance > > predictability of different cgroups that share the same block devices. > > We should get an IO controller into Linux. Does anyone have a reason > why it shouldn't be this one? > > > Respect to other priority/weight-based solutions the approach used by > > this controller is to explicitly choke applications' requests > > Yes, blocking the offending application at a high level has always > seemed to me to be the best way of implementing the controller. > > > that > > directly or indirectly generate IO activity in the system (this > > controller addresses both synchronous IO and writeback/buffered IO). > > The problem I've seen with some of the proposed controllers was that > they didn't handle delayed writeback very well, if at all. > > Can you explain at a high level but in some detail how this works? If > an application is doing a huge write(), how is that detected and how is > the application made to throttle? The writeback writes are handled in three steps: 1) track the owner of the dirty pages 2) detect writeback IO 3) delay writeback IO that exceeds the cgroup limits For 1) I barely used the bio-cgroup functionality. The bio-cgroup use the page_cgroup structure to store the owner of each dirty page when the page is dirtied. At this point the actual owner of the page can be retrieved looking at current->mm->owner (i.e. in __set_page_dirty()), and its bio_cgroup id is stored into the page_cgroup structure. Then for 2) we can detect writeback IO placing a hook, cgroup_io_throttle(), in submit_bio(): unsigned long long cgroup_io_throttle(struct bio *bio, struct block_device *bdev, ssize_t bytes); If the IO operation is a write we look at the owner of the pages involved (from bio) and we check if we must throttle the operation. If the owner of that page is "current", we throttle the current task directly (via schedule_timeout_killable()) and we just return 0 from cgroup_io_throttle() after the sleep. 3) If the owner of the page must be throttled and the current task is not the same task, e.g., it's a kernel thread (current->flags & (PF_KTHREAD | PF_FLUSHER | PF_KSWAPD)), then we assume it's a writeback IO and we immediately return the amount of jiffies that the real owner should sleep. void submit_bio(int rw, struct bio *bio) { ... if (bio_has_data(bio)) { unsigned long sleep = 0; if (rw & WRITE) { count_vm_events(PGPGOUT, count); sleep = cgroup_io_throttle(bio, bio->bi_bdev, bio->bi_size); } else { task_io_account_read(bio->bi_size); count_vm_events(PGPGIN, count); cgroup_io_throttle(NULL, bio->bi_bdev, bio->bi_size); } ... if (sleep && !iothrottle_make_request(bio, jiffies + sleep)) return; } generic_make_request(bio); ... } Since the current task must not be throttled here, we set a deadline jiffies + sleep and we add this request in a rbtree via iothrottle_make_request(). This request will be dispatched ansychronously by a kernel thread - kiothrottled() - using generic_make_request() when the deadline will expire. There's a lot of space for optimizations here, i.e. use many threads per block device, workqueue, slow-work, ... In the old version (v12) I simply throttled writeback IO in balance_dirty_pages_ratelimited_nr() but this obviously leads to bursty writebacks. In v13 the writeback IO is hugely more smooth. > > Does it add new metadata to `struct page' for this? struct page_cgroup > > I assume that the write throttling is also wired up into the MAP_SHARED > write-fault path? > mmmh.. in case of writeback IO we account and throttle requests for mm->owner. In case of synchronous IO (read/write) we always throttle the current task in submit_bio(). > > > Does this patchset provide a path by which we can implement IO control > for (say) NFS mounts? Honestly I didn't looked at all at this. :) I'll check, but in principle adding the cgroup_io_throttle() hook in the opportune NFS path is enough to provide IO control also for NFS mounts. -Andrea -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/