linux-kernel - Re: [PATCH 44/49] mm: numa: Add THP migration for the NUMA working set scanning fault case.

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Date:	Mon, 7 Jan 2013 15:37:23 +0000
From:	Mel Gorman <mgorman@...e.de>
To:	Wanpeng Li <liwanp@...ux.vnet.ibm.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Ingo Molnar <mingo@...nel.org>, Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Hugh Dickins <hughd@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Paul Turner <pjt@...gle.com>, Hillf Danton <dhillf@...il.com>,
	David Rientjes <rientjes@...gle.com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Alex Shi <lkml.alex@...il.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Aneesh Kumar <aneesh.kumar@...ux.vnet.ibm.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 44/49] mm: numa: Add THP migration for the NUMA working
 set scanning fault case.

On Sat, Jan 05, 2013 at 04:42:29PM +0800, Wanpeng Li wrote:
> >+int numamigrate_isolate_page(pg_data_t *pgdat, struct page *page)
> >+{
> >+	int ret = 0;
> >
> > 	/* Avoid migrating to a node that is nearly full */
> > 	if (migrate_balanced_pgdat(pgdat, 1)) {
> 
> Hi Mel Gorman,
> 
> This parameter nr_migrate_pags = 1 is not correct, since balancenuma also 
> support THP in this patchset, the parameter should be 1 <= compound_order(page) 
> instead of 1. I'd rather change to something like:
> 

True. The impact is marginal because it only applies when a node is almost
full but it does mean that we do some unnecessary work before migration
fails anyway. I've added a TODO item to fix it when I next revisit NUMA
balancing. Thanks.

-- 
Mel Gorman
SUSE Labs
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