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

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Message-ID: <8761a0arki.fsf@linux.vnet.ibm.com>
Date:	Tue, 17 Mar 2015 15:12:05 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>
Cc:	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>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>,
	Jerome Marchand <jmarchan@...hat.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCHv4 00/24] THP refcounting redesign

"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com> writes:

> 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 tested this patch on ppc64 and verified thp allocation and split.
I also checked the subpage_prot and it worked as expected. I will
run more tests with this series and update if I find any issues.

-aneesh

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