linux-kernel - Pagecache: find_or_create_page does not call a proper page allocator function

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Message-ID: <Pine.LNX.4.64.0704231408530.691@schroedinger.engr.sgi.com>
Date:	Mon, 23 Apr 2007 14:11:57 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Nick Piggin <npiggin@...e.de>
cc:	linux-kernel@...r.kernel.org, pj@....com,
	akpm@...ux-foundation.org, Hugh Dickins <hugh@...itas.com>
Subject: Pagecache: find_or_create_page does not call a proper page allocator
 function

The find_or_create function calls alloc_page with a local gfp mask instead
of using page_cache_alloc. This means that the page allocation will not
obey cpuset memory spreading and page allocation will not properly use the
gfp flags in the address space. Highmem is not set correctly.

It turns out that there is no function to allocate a page for the page cache
with a gfp mask. So we create one ORing the context gfp flags with the gfp flags
from the mapping.

Signed-off-by: Christoph Lameter <clameter@....com>

---
 include/linux/pagemap.h |   10 ++++++++--
 mm/filemap.c            |    3 ++-
 2 files changed, 10 insertions(+), 3 deletions(-)

Index: linux-2.6.21-rc7/include/linux/pagemap.h
===================================================================
--- linux-2.6.21-rc7.orig/include/linux/pagemap.h	2007-04-23 13:52:20.000000000 -0700
+++ linux-2.6.21-rc7/include/linux/pagemap.h	2007-04-23 14:01:09.000000000 -0700
@@ -60,14 +60,20 @@ static inline struct page *__page_cache_
 }
 #endif
 
+static inline struct page *page_cache_alloc_mask(struct address_space *x,
+			gfp_t gfp)
+{
+	return __page_cache_alloc(mapping_gfp_mask(x) | gfp);
+}
+
 static inline struct page *page_cache_alloc(struct address_space *x)
 {
-	return __page_cache_alloc(mapping_gfp_mask(x));
+	return page_cache_alloc_mask(x, 0);
 }
 
 static inline struct page *page_cache_alloc_cold(struct address_space *x)
 {
-	return __page_cache_alloc(mapping_gfp_mask(x)|__GFP_COLD);
+	return page_cache_alloc_mask(x, __GFP_COLD);
 }
 
 typedef int filler_t(void *, struct page *);
Index: linux-2.6.21-rc7/mm/filemap.c
===================================================================
--- linux-2.6.21-rc7.orig/mm/filemap.c	2007-04-23 13:50:24.000000000 -0700
+++ linux-2.6.21-rc7/mm/filemap.c	2007-04-23 13:52:14.000000000 -0700
@@ -670,7 +670,8 @@ repeat:
 	page = find_lock_page(mapping, index);
 	if (!page) {
 		if (!cached_page) {
-			cached_page = alloc_page(gfp_mask);
+			cached_page =
+				page_cache_alloc_mask(mapping, gfp_mask);
 			if (!cached_page)
 				return NULL;
 		}
-
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