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Date: Wed, 3 Feb 2016 14:43:16 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: Dave Hansen <dave.hansen@intel.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Hugh Dickins <hughd@google.com>, Mel Gorman <mgorman@suse.de>,
        Rik van Riel <riel@redhat.com>, Vlastimil Babka <vbabka@suse.cz>,
        Christoph Lameter <cl@gentwo.org>,
        Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
        Steve Capper <steve.capper@linaro.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
        Johannes Weiner <hannes@cmpxchg.org>, Michal Hocko <mhocko@suse.cz>,
        Jerome Marchand <jmarchan@redhat.com>,
        Sasha Levin <sasha.levin@oracle.com>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
Subject: Re: [PATCH 4/4] thp: rewrite freeze_page()/unfreeze_page() with
 generic rmap walkers
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On Wed, 3 Feb 2016 07:42:01 -0800 Dave Hansen <dave.hansen@intel.com> wrote:

> 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?

yup.  And the "more testing is required" is a bit worrisome.  Is this
code really ready for getting pounded upon in -next?