linux-kernel - Re: [PATCH 01/28] mm, page_alloc: Only check PageCompound for high-order pages

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Message-ID: <571F4EED.2060208@suse.cz>
Date:	Tue, 26 Apr 2016 13:20:13 +0200
From:	Vlastimil Babka <vbabka@...e.cz>
To:	Mel Gorman <mgorman@...hsingularity.net>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Jesper Dangaard Brouer <brouer@...hat.com>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 01/28] mm, page_alloc: Only check PageCompound for
 high-order pages

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.