linux-kernel - Re: [PATCH 4/4] thp: rewrite freeze_page()/unfreeze

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Date:	Wed, 3 Feb 2016 07:42:01 -0800
From:	Dave Hansen <dave.hansen@...el.com>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>
Cc:	Hugh Dickins <hughd@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Rik van Riel <riel@...hat.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Christoph Lameter <cl@...two.org>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Steve Capper <steve.capper@...aro.org>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>,
	Jerome Marchand <jmarchan@...hat.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 4/4] thp: rewrite freeze_page()/unfreeze_page() with
 generic rmap walkers

On 02/03/2016 07:14 AM, Kirill A. Shutemov wrote:
> But the new variant is somewhat slower. Current helpers iterates over
> VMAs the compound page is mapped to, and then over ptes within this VMA.
> New helpers iterates over small page, then over VMA the small page
> mapped to, and only then find relevant pte.

The code simplification here is really attractive.  Can you quantify
what the slowdown is?  Is it noticeable, or would it be in the noise
during all the other stuff that happens under memory pressure?