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

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Message-ID: <20160203225304.GB22605@black.fi.intel.com>
Date:	Thu, 4 Feb 2016 01:53:04 +0300
From:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Dave Hansen <dave.hansen@...el.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	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 Wed, Feb 03, 2016 at 02:43:16PM -0800, Andrew Morton wrote:
> On Wed, 3 Feb 2016 07:42:01 -0800 Dave Hansen <dave.hansen@...el.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.

It is not really clear, how to quantify this properly. Let me think more
about it.

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

By now it survived 5+ hours of fuzzing in 16 VM in parallel. I'll continue
with other tests tomorrow.

-- 
 Kirill A. Shutemov