linux-kernel - Re: [PATCHv5 00/28] THP refcounting redesign

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Message-Id: <20150427160348.fa3aefc5fc557e429d6b0295@linux-foundation.org>
Date:	Mon, 27 Apr 2015 16:03:48 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:	Andrea Arcangeli <aarcange@...hat.com>,
	Hugh Dickins <hughd@...gle.com>,
	Dave Hansen <dave.hansen@...el.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: [PATCHv5 00/28] THP refcounting redesign

On Fri, 24 Apr 2015 00:03:35 +0300 "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com> wrote:

> Hello everybody,
> 
> Here's reworked version of my patchset. All known issues were addressed.
> 
> 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.

Are there any measurable performance improvements?

> 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.
> 
> The patchset drastically lower complexity of get_page()/put_page()
> codepaths. I encourage reviewers look on this code before-and-after to
> justify time budget on reviewing this patchset.
>
> ...
>
>  59 files changed, 1144 insertions(+), 1509 deletions(-)

It's huge.  I'm going to need help reviewing this.  Have earlier
versions been reviewed much?  Who do you believe are suitable
reviewers?
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