linux-kernel - Re: [PATCHv4 00/24] THP refcounting redesign

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Message-ID: <20150305160426.GA20370@node.dhcp.inet.fi>
Date:	Thu, 5 Mar 2015 18:04:26 +0200
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Jerome Marchand <jmarchan@...hat.com>
Cc:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Dave Hansen <dave.hansen@...el.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>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCHv4 00/24] THP refcounting redesign

On Thu, Mar 05, 2015 at 01:55:15PM +0100, Jerome Marchand wrote:
> On 03/04/2015 05:32 PM, Kirill A. Shutemov wrote:
> > Hello everybody,
> > 
> > It's bug-fix update of my thp refcounting work.
> > 
> > The goal of patchset is to make refcounting on THP pages cheaper with
> > simpler semantics and allow the same THP compound page to be mapped with
> > PMD and PTEs. This is required to get reasonable THP-pagecache
> > implementation.
> > 
> > With the new refcounting design it's much easier to protect against
> > split_huge_page(): simple reference on a page will make you the deal.
> > It makes gup_fast() implementation simpler and doesn't require
> > special-case in futex code to handle tail THP pages.
> > 
> > It should improve THP utilization over the system since splitting THP in
> > one process doesn't necessary lead to splitting the page in all other
> > processes have the page mapped.
> > 
> [...]
> > I believe all known bugs have been fixed, but I'm sure Sasha will bring more
> > reports.
> > 
> > The patchset also available on git:
> > 
> > git://git.kernel.org/pub/scm/linux/kernel/git/kas/linux.git thp/refcounting/v4
> > 
> 
> Hi Kirill,
> 
> I ran some ltp tests and it triggered two bugs:

Okay. The root of both is change in page_mapped(). I'll think how to fix
this.

-- 
 Kirill A. Shutemov
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