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Subject: Re: [PATCH 01/28] mm, page_alloc: Only check PageCompound for
 high-order pages
To: Mel Gorman <mgorman@techsingularity.net>
References: <1460710760-32601-1-git-send-email-mgorman@techsingularity.net>
 <1460710760-32601-2-git-send-email-mgorman@techsingularity.net>
 <571DE45B.2050504@suse.cz> <20160426103334.GB2858@techsingularity.net>
Cc: Andrew Morton <akpm@linux-foundation.org>,
        Jesper Dangaard Brouer <brouer@redhat.com>,
        Linux-MM <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>
From: Vlastimil Babka <vbabka@suse.cz>
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Date: Tue, 26 Apr 2016 13:20:13 +0200
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On 04/26/2016 12:33 PM, Mel Gorman wrote:
>
> I dithered on this a bit and could not convince myself that the order
> case really is unlikely. It depends on the situation as we could be
> tearing down a large THP-backed mapping. SLUB is also using compound
> pages so it's both workload and configuration dependent whether this
> path is really likely or not.

Hmm I see. But e.g. buffered_rmqueue uses "if (likely(order == 0))" so it would 
be at least consistent. Also compound pages can amortize the extra cost over 
more base pages.