linux-kernel - Re: [PATCH 1/2] Revert "mm: make faultaround produce old ptes"

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Message-ID: <20160616151049.GM6836@dhcp22.suse.cz>
Date:	Thu, 16 Jun 2016 17:10:49 +0200
From:	Michal Hocko <mhocko@...nel.org>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mgorman@...e.de>,
	"Huang, Ying" <ying.huang@...el.com>,
	Minchan Kim <minchan@...nel.org>,
	Vinayak Menon <vinmenon@...eaurora.org>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 1/2] Revert "mm: make faultaround produce old ptes"

On Thu 16-06-16 15:27:35, Kirill A. Shutemov wrote:
> On Thu, Jun 16, 2016 at 02:20:02PM +0200, Michal Hocko wrote:
> > On Tue 14-06-16 11:42:29, Kirill A. Shutemov wrote:
> > > This reverts commit 5c0a85fad949212b3e059692deecdeed74ae7ec7.
> > > 
> > > The commit causes ~6% regression in unixbench.
> > 
> > Is the regression fully explained? My understanding from the email
> > thread is that this is suspiciously too high. It is not like I would
> > be against the revert but having an explanation would be really
> > appreciated.
> 
> My understanding is that it's overhead on setting accessed bit:
> 
> http://lkml.kernel.org/r/20160613125248.GA30109@black.fi.intel.com

But those numbers cannot explain the regression completely AFAIU. It
smells like something else is going on. Anyway, as I've said I do not
have anything against the revert just more than "unixbench regresses"
would be nice.
-- 
Michal Hocko
SUSE Labs