From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail6.bemta7.messagelabs.com (mail6.bemta7.messagelabs.com [216.82.255.55]) by kanga.kvack.org (Postfix) with ESMTP id 582726B016A for ; Tue, 6 Sep 2011 20:17:47 -0400 (EDT) Date: Wed, 7 Sep 2011 02:17:42 +0200 From: Jan Kara Subject: Re: [PATCH 15/18] writeback: charge leaked page dirties to active tasks Message-ID: <20110907001742.GE31945@quack.suse.cz> References: <20110904015305.367445271@intel.com> <20110904020916.588150387@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110904020916.588150387@intel.com> Sender: owner-linux-mm@kvack.org List-ID: To: Wu Fengguang Cc: linux-fsdevel@vger.kernel.org, Peter Zijlstra , Andrew Morton , Jan Kara , Christoph Hellwig , Dave Chinner , Greg Thelen , Minchan Kim , Vivek Goyal , Andrea Righi , linux-mm , LKML On Sun 04-09-11 09:53:20, Wu Fengguang wrote: > It's a years long problem that a large number of short-lived dirtiers > (eg. gcc instances in a fast kernel build) may starve long-run dirtiers > (eg. dd) as well as pushing the dirty pages to the global hard limit. I don't think it's years long problem. When we do per-cpu ratelimiting, short lived processes have the same chance (proportional to the number of pages dirtied) of hitting balance_dirty_pages() as long-run dirtiers have. So this problem seems to be introduced by your per task dirty ratelimiting? But given that you kept per-cpu ratelimiting in the end, is this still an issue? Do you have some numbers for this patch? Honza > The solution is to charge the pages dirtied by the exited gcc to the > other random gcc/dd instances. It sounds not perfect, however should > behave good enough in practice. > > CC: Peter Zijlstra > Signed-off-by: Wu Fengguang > --- > include/linux/writeback.h | 2 ++ > kernel/exit.c | 2 ++ > mm/page-writeback.c | 12 ++++++++++++ > 3 files changed, 16 insertions(+) > > --- linux-next.orig/include/linux/writeback.h 2011-08-29 19:14:22.000000000 +0800 > +++ linux-next/include/linux/writeback.h 2011-08-29 19:14:32.000000000 +0800 > @@ -7,6 +7,8 @@ > #include > #include > > +DECLARE_PER_CPU(int, dirty_leaks); > + > /* > * The 1/4 region under the global dirty thresh is for smooth dirty throttling: > * > --- linux-next.orig/mm/page-writeback.c 2011-08-29 19:14:22.000000000 +0800 > +++ linux-next/mm/page-writeback.c 2011-08-29 19:14:32.000000000 +0800 > @@ -1237,6 +1237,7 @@ void set_page_dirty_balance(struct page > } > > static DEFINE_PER_CPU(int, bdp_ratelimits); > +DEFINE_PER_CPU(int, dirty_leaks) = 0; > > /** > * balance_dirty_pages_ratelimited_nr - balance dirty memory state > @@ -1285,6 +1286,17 @@ void balance_dirty_pages_ratelimited_nr( > ratelimit = 0; > } > } > + /* > + * Pick up the dirtied pages by the exited tasks. This avoids lots of > + * short-lived tasks (eg. gcc invocations in a kernel build) escaping > + * the dirty throttling and livelock other long-run dirtiers. > + */ > + p = &__get_cpu_var(dirty_leaks); > + if (*p > 0 && current->nr_dirtied < ratelimit) { > + nr_pages_dirtied = min(*p, ratelimit - current->nr_dirtied); > + *p -= nr_pages_dirtied; > + current->nr_dirtied += nr_pages_dirtied; > + } > preempt_enable(); > > if (unlikely(current->nr_dirtied >= ratelimit)) > --- linux-next.orig/kernel/exit.c 2011-08-26 16:19:27.000000000 +0800 > +++ linux-next/kernel/exit.c 2011-08-29 19:14:22.000000000 +0800 > @@ -1044,6 +1044,8 @@ NORET_TYPE void do_exit(long code) > validate_creds_for_do_exit(tsk); > > preempt_disable(); > + if (tsk->nr_dirtied) > + __this_cpu_add(dirty_leaks, tsk->nr_dirtied); > exit_rcu(); > /* causes final put_task_struct in finish_task_switch(). */ > tsk->state = TASK_DEAD; > > -- Jan Kara SUSE Labs, CR -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org