linux-kernel - [PATCH 2/4] mm: hugetlbfs_pagecache

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Date:	Tue, 15 Sep 2009 21:33:02 +0100 (BST)
From:	Hugh Dickins <hugh.dickins@...cali.co.uk>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>, Rik van Riel <riel@...hat.com>,
	Mel Gorman <mel@....ul.ie>,
	Minchan Kim <minchan.kim@...il.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: [PATCH 2/4] mm: hugetlbfs_pagecache_present

Rename hugetlbfs_backed() to hugetlbfs_pagecache_present()
and add more comments, as suggested by Mel Gorman.

Signed-off-by: Hugh Dickins <hugh.dickins@...cali.co.uk>
---

 mm/hugetlb.c |   16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

--- mm1/mm/hugetlb.c	2009-09-14 16:34:37.000000000 +0100
+++ mm2/mm/hugetlb.c	2009-09-15 17:32:12.000000000 +0100
@@ -2016,8 +2016,11 @@ static struct page *hugetlbfs_pagecache_
 	return find_lock_page(mapping, idx);
 }
 
-/* Return whether there is a pagecache page to back given address within VMA */
-static bool hugetlbfs_backed(struct hstate *h,
+/*
+ * Return whether there is a pagecache page to back given address within VMA.
+ * Caller follow_hugetlb_page() holds page_table_lock so we cannot lock_page.
+ */
+static bool hugetlbfs_pagecache_present(struct hstate *h,
 			struct vm_area_struct *vma, unsigned long address)
 {
 	struct address_space *mapping;
@@ -2254,10 +2257,13 @@ int follow_hugetlb_page(struct mm_struct
 
 		/*
 		 * When coredumping, it suits get_dump_page if we just return
-		 * an error if there's a hole and no huge pagecache to back it.
+		 * an error where there's an empty slot with no huge pagecache
+		 * to back it.  This way, we avoid allocating a hugepage, and
+		 * the sparse dumpfile avoids allocating disk blocks, but its
+		 * huge holes still show up with zeroes where they need to be.
 		 */
-		if (absent &&
-		    ((flags & FOLL_DUMP) && !hugetlbfs_backed(h, vma, vaddr))) {
+		if (absent && (flags & FOLL_DUMP) &&
+		    !hugetlbfs_pagecache_present(h, vma, vaddr)) {
 			remainder = 0;
 			break;
 		}
--
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