linux-kernel - Re: [patch v2] mm, tmp: only collapse hugepages to nodes with affinity for zone_reclaim

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Message-ID: <alpine.DEB.2.02.1407161754000.23892@chino.kir.corp.google.com>
Date:	Wed, 16 Jul 2014 17:54:20 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Vlastimil Babka <vbabka@...e.cz>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Bob Liu <bob.liu@...cle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch v2] mm, tmp: only collapse hugepages to nodes with affinity
 for zone_reclaim_mode

On Wed, 16 Jul 2014, Vlastimil Babka wrote:

> I wonder if you could do this here?
> 
> if (khugepaged_node_load[nid])
> 	return false;
> 
> If the condition is true, it means you already checked the 'nid' node against
> all other nodes present in the pmd in a previous khugepaged_scan_pmd iteration.
> And if it passed then, it would also pass now. If meanwhile a new node was found
> and recorded, it was also checked against everything present at that point,
> including 'nid'. So it should be safe?
> 
> The worst case (perfect interleaving page per page, so that "node != last_node"
> is true in each iteration) complexity then reduces from O(HPAGE_PMD_NR *
> MAX_NUMNODES) to O(HPAGE_PMD_NR + MAX_NUMNODES) iterations.
> 

Excellent suggestion, thanks Vlastimil!
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