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

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Message-ID: <Pine.LNX.4.64.0704231541180.975@schroedinger.engr.sgi.com>
Date:	Mon, 23 Apr 2007 15:42:11 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Nick Piggin <npiggin@...e.de>, linux-kernel@...r.kernel.org,
	pj@....com, Hugh Dickins <hugh@...itas.com>
Subject: Re: Pagecache: find_or_create_page does not call a proper page
 allocator function

And the second fix (cleanup patch will follow)

Pagecache: find_or_create_page does not spread memory.

The find_or_create function calls alloc_page with the gfp_mask passed to it
which is derived from the mappings gfp mask. So the allocation flags are right
(assuming my bugfix to fs/buffer.c is applied).

However, we call a alloc_page instead of page_cache_alloc in find_or_create_page.
This means that the page cache allocation will not obey cpuset memory spreading.

We really need to call __page_cache_alloc there.

Also stick a comment in there explaining how the allocation mask passed to
find_or_create_page needs to be handled.

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

---
 mm/filemap.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

Index: linux-2.6.21-rc7/mm/filemap.c
===================================================================
--- linux-2.6.21-rc7.orig/mm/filemap.c	2007-04-23 15:37:27.000000000 -0700
+++ linux-2.6.21-rc7/mm/filemap.c	2007-04-23 15:38:09.000000000 -0700
@@ -648,7 +648,8 @@ EXPORT_SYMBOL(find_lock_page);
  * find_or_create_page - locate or add a pagecache page
  * @mapping: the page's address_space
  * @index: the page's index into the mapping
- * @gfp_mask: page allocation mode
+ * @gfp_mask: page allocation mode. This must be derived from the
+ * 	allocation flags of the mapping!
  *
  * Locates a page in the pagecache.  If the page is not present, a new page
  * is allocated using @gfp_mask and is added to the pagecache and to the VM's
@@ -670,7 +671,8 @@ repeat:
 	page = find_lock_page(mapping, index);
 	if (!page) {
 		if (!cached_page) {
-			cached_page = alloc_page(gfp_mask);
+			cached_page =
+				__page_cache_alloc(gfp_mask);
 			if (!cached_page)
 				return NULL;
 		}
-
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