linux-kernel - Re: [PATCHv6 00/36] THP refcounting redesign

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20150622133917.GA8398@node.dhcp.inet.fi>
Date:	Mon, 22 Jun 2015 16:39:17 +0300
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>,
	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>,
	Sasha Levin <sasha.levin@...cle.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCHv6 00/36] THP refcounting redesign

On Mon, Jun 22, 2015 at 03:32:54PM +0200, Jerome Marchand wrote:
> On 06/22/2015 03:21 PM, Kirill A. Shutemov wrote:
> > On Tue, Jun 16, 2015 at 03:17:13PM +0200, Jerome Marchand wrote:
> >> On 06/03/2015 07:05 PM, Kirill A. Shutemov wrote:
> >>> Hello everybody,
> >>>
> >>> Here's new revision of refcounting patchset. Please review and consider
> >>> applying.
> >>>
> >>> 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.
> >>>
> >>> The patchset drastically lower complexity of get_page()/put_page()
> >>> codepaths. I encourage people look on this code before-and-after to
> >>> justify time budget on reviewing this patchset.
> >>>
> >>> = Changelog =
> >>>
> >>> v6:
> >>>   - rebase to since-4.0;
> >>>   - optimize mapcount handling: significantely reduce overhead for most
> >>>     common cases.
> >>>   - split pages on migrate_pages();
> >>>   - remove infrastructure for handling splitting PMDs on all architectures;
> >>>   - fix page_mapcount() for hugetlb pages;
> >>>
> >>
> >> Hi Kirill,
> >>
> >> I ran some LTP mm tests and hugemmap tests trigger the following:
> >>
> >> [  438.749457] page:ffffea0000df8000 count:2 mapcount:0 mapping:          (null) index:0x0 compound_mapcount: 0
> >> [  438.750089] flags: 0x3ffc0000004001(locked|head)
> >> [  438.750089] page dumped because: VM_BUG_ON_PAGE(page_mapped(page))
> > 
> > Did you run with original or updated version of patch 27/36?
> > In original post of v6 there was bug: page_mapped() always returned true.
> > 
> 
> Indeed! I'll try again with the corrected patch.

I'm going to post updated patchset soon. Probably tomorrow.

-- 
 Kirill A. Shutemov
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
Please read the FAQ at  http://www.tux.org/lkml/