From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx191.postini.com [74.125.245.191]) by kanga.kvack.org (Postfix) with SMTP id AFDED6B0033 for ; Wed, 28 Aug 2013 12:41:18 -0400 (EDT) Date: Wed, 28 Aug 2013 18:41:00 +0200 From: Peter Zijlstra Subject: Re: [PATCH -v3] sched, numa: Use {cpu, pid} to create task groups for shared faults Message-ID: <20130828164100.GS10002@twins.programming.kicks-ass.net> References: <1373901620-2021-1-git-send-email-mgorman@suse.de> <20130730113857.GR3008@twins.programming.kicks-ass.net> <20130731150751.GA15144@twins.programming.kicks-ass.net> <51F93105.8020503@hp.com> <20130802164715.GP27162@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130802164715.GP27162@twins.programming.kicks-ass.net> Sender: owner-linux-mm@kvack.org List-ID: To: Don Morris Cc: Mel Gorman , Srikar Dronamraju , Ingo Molnar , Andrea Arcangeli , Johannes Weiner , Linux-MM , LKML , riel@redhat.com On Fri, Aug 02, 2013 at 06:47:15PM +0200, Peter Zijlstra wrote: > Subject: sched, numa: Use {cpu, pid} to create task groups for shared faults > From: Peter Zijlstra > Date: Tue Jul 30 10:40:20 CEST 2013 > > A very simple/straight forward shared fault task grouping > implementation. > > Signed-off-by: Peter Zijlstra So Rik and me found a possible issue with this -- although in the end it turned out to be a userspace 'feature' instead. It might be possible for a COW page to be 'shared' and thus get a last_cpupid set from another process. When we break cow and reuse the now private and writable page might still have this last_cpupid and thus cause a shared fault and form grouping. Something like the below resets the last_cpupid field on reuse much like fresh COW copies will have. There might be something that avoids the above scenario but I'm too tired to come up with anything. --- --- a/mm/memory.c +++ b/mm/memory.c @@ -2730,6 +2730,9 @@ static int do_wp_page(struct mm_struct * get_page(dirty_page); reuse: + if (old_page) + page_cpupid_xchg_last(old_page, (1 << LAST_CPUPID_SHIFT) - 1); + flush_cache_page(vma, address, pte_pfn(orig_pte)); entry = pte_mkyoung(orig_pte); entry = maybe_mkwrite(pte_mkdirty(entry), vma); -- 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