linux-kernel - RE: [PATCH 32/36] thp: reintroduce split_huge

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Message-Id: <20150714140457.AD1338B@black.fi.intel.com>
Date:	Tue, 14 Jul 2015 17:04:57 +0300 (EEST)
From:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:	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>,
	Jerome Marchand <jmarchan@...hat.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: RE: [PATCH 32/36] thp: reintroduce split_huge_page()

Kirill A. Shutemov wrote:
> This patch adds implementation of split_huge_page() for new
> refcountings.
> 
> Unlike previous implementation, new split_huge_page() can fail if
> somebody holds GUP pin on the page. It also means that pin on page
> would prevent it from bening split under you. It makes situation in
> many places much cleaner.
> 
> The basic scheme of split_huge_page():
> 
>   - Check that sum of mapcounts of all subpage is equal to page_count()
>     plus one (caller pin). Foll off with -EBUSY. This way we can avoid
>     useless PMD-splits.
> 
>   - Freeze the page counters by splitting all PMD and setup migration
>     PTEs.
> 
>   - Re-check sum of mapcounts against page_count(). Page's counts are
>     stable now. -EBUSY if page is pinned.
> 
>   - Split compound page.
> 
>   - Unfreeze the page by removing migration entries.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Tested-by: Sasha Levin <sasha.levin@...cle.com>

checkpatch fixlet:

749ab1c0df4a thp: reintroduce split_huge_page() fix
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 5df1b76837c7..a200ed579e1f 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2998,7 +2998,7 @@ static void __split_huge_page(struct page *page, struct list_head *list)
  * Both head page and tail pages will inherit mapping, flags, and so on from
  * the hugepage.
  *
- * GUP pin and PG_locked transfered to @page. Rest subpages can be freed if
+ * GUP pin and PG_locked transferred to @page. Rest subpages can be freed if
  * they are not mapped.
  *
  * Returns 0 if the hugepage is split successfully.
--
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