From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-io0-f198.google.com (mail-io0-f198.google.com [209.85.223.198]) by kanga.kvack.org (Postfix) with ESMTP id 8DC396B02A4 for ; Thu, 22 Feb 2018 04:40:15 -0500 (EST) Received: by mail-io0-f198.google.com with SMTP id 62so4112906iow.16 for ; Thu, 22 Feb 2018 01:40:15 -0800 (PST) Received: from merlin.infradead.org (merlin.infradead.org. [2001:8b0:10b:1231::1]) by mx.google.com with ESMTPS id h184si1367923ioe.132.2018.02.22.01.40.14 for (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Thu, 22 Feb 2018 01:40:14 -0800 (PST) Date: Thu, 22 Feb 2018 10:40:09 +0100 From: Peter Zijlstra Subject: Re: [PATCH] Synchronize task mm counters on context switch Message-ID: <20180222094009.GO25201@hirez.programming.kicks-ass.net> References: <20180205220325.197241-1-dancol@google.com> <20180222001635.GB27147@rodete-desktop-imager.corp.google.com> <20180222020633.GC27147@rodete-desktop-imager.corp.google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180222020633.GC27147@rodete-desktop-imager.corp.google.com> Sender: owner-linux-mm@kvack.org List-ID: To: Minchan Kim Cc: Daniel Colascione , linux-mm@kvack.org, Andrew Morton , Oleg Nesterov , Michal Hocko On Thu, Feb 22, 2018 at 11:06:33AM +0900, Minchan Kim wrote: > On Wed, Feb 21, 2018 at 04:23:43PM -0800, Daniel Colascione wrote: > > kernel/sched/core.c | 3 +++ > > 1 file changed, 3 insertions(+) > > > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > > index a7bf32aabfda..7f197a7698ee 100644 > > --- a/kernel/sched/core.c > > +++ b/kernel/sched/core.c > > @@ -3429,6 +3429,9 @@ asmlinkage __visible void __sched schedule(void) > > struct task_struct *tsk = current; > > > > sched_submit_work(tsk); > > + if (tsk->mm) > > + sync_mm_rss(tsk->mm); > > + > > do { > > preempt_disable(); > > __schedule(false); > > Obviously I completely hate that; and you really _should_ have Cc'ed me earlier ;-) That it still well over 100 cycles in the case when all counters did change. Far _far_ more if the mm counters are contended (up to 150 times more is quite possible). > > > > Ping? Is this approach just a bad idea? We could instead just manually sync > > > > all mm-attached tasks at counter-retrieval time. > > > > > > IMHO, yes, it should be done when user want to see which would be really > > > cold path while this shecule function is hot. > > > > > > > The problem with doing it that way is that we need to look at each task > > attached to a particular mm. AFAIK (and please tell me if I'm wrong), the > > only way to do that is to iterate over all processes, and for each process > > attached to the mm we want, iterate over all its tasks (since each one has > > to have the same mm, I think). Does that sound right? You could just iterate the thread group and call it a day. Yes strictly speaking its possible to have mm's shared outside the thread group, practically that 'never' happens. CLONE_VM without CLONE_THREAD just isn't a popular thing afaik. So while its not perfect, it might well be good enough. -- 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/ . Don't email: email@kvack.org