linux-kernel - Re: [PATCHv9 34/36] thp: introduce deferred_split_huge

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Message-ID: <55BB90F1.9000809@redhat.com>
Date:	Fri, 31 Jul 2015 17:14:57 +0200
From:	Jerome Marchand <jmarchan@...hat.com>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Hugh Dickins <hughd@...gle.com>
CC:	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: [PATCHv9 34/36] thp: introduce deferred_split_huge_page()

On 07/20/2015 04:21 PM, Kirill A. Shutemov wrote:
> Currently we don't split huge page on partial unmap. It's not an ideal
> situation. It can lead to memory overhead.
> 
> Furtunately, we can detect partial unmap on page_remove_rmap(). But we
> cannot call split_huge_page() from there due to locking context.
> 
> It's also counterproductive to do directly from munmap() codepath: in
> many cases we will hit this from exit(2) and splitting the huge page
> just to free it up in small pages is not what we really want.
> 
> The patch introduce deferred_split_huge_page() which put the huge page
> into queue for splitting. The splitting itself will happen when we get
> memory pressure via shrinker interface. The page will be dropped from
> list on freeing through compound page destructor.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Tested-by: Sasha Levin <sasha.levin@...cle.com>
> Tested-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
> Acked-by: Vlastimil Babka <vbabka@...e.cz>

Acked-by: Jerome Marchand <jmarchan@...hat.com>

> ---
>  include/linux/huge_mm.h |   4 ++
>  include/linux/mm.h      |   2 +
>  mm/huge_memory.c        | 127 ++++++++++++++++++++++++++++++++++++++++++++++--
>  mm/migrate.c            |   1 +
>  mm/page_alloc.c         |   2 +-
>  mm/rmap.c               |   7 ++-
>  6 files changed, 138 insertions(+), 5 deletions(-)
>



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