From: Hugh Dickins <hugh@veritas.com>
A small change to the tests for "Bad page state", to avoid one class of the
page_remove_rmap BUG reports, giving more information while letting the
system continue: check page_mapcount (_mapcount != -1) rather than
page_mapped (_mapcount >= 0).
And how does _mapcount go bad? In the case under study, it looks sure now
that an overheating(?) Pentium III sometimes gets confused by a pair of
instructions in the no-buddy-bitmap __free_pages_bulk, and clears the
PG_private bit from the _mapcount field while buddying around - changing
PG_private value changes the bit cleared from _mapcount. Bad page state
mapcount:-4096 would have tracked this down much sooner, and will be
recognizable if other cpus show the same aberrant reaction to 2.6.11.
The page_remove_rmap BUG does need to be replaced by more permissive and
informative handling, but I'm not yet ready to to finalize such a patch.
Please admit Colin Harrison to the Order of the Iridescent Penguin, for his
tireless testing.
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---
25-akpm/mm/page_alloc.c | 4 ++--
1 files changed, 2 insertions(+), 2 deletions(-)
diff -puN mm/page_alloc.c~bad-page-state-mapcount mm/page_alloc.c
--- 25/mm/page_alloc.c~bad-page-state-mapcount 2005-03-07 20:41:24.000000000 -0800
+++ 25-akpm/mm/page_alloc.c 2005-03-07 20:41:24.000000000 -0800
@@ -306,7 +306,7 @@ static inline void __free_pages_bulk (st
static inline void free_pages_check(const char *function, struct page *page)
{
- if ( page_mapped(page) ||
+ if ( page_mapcount(page) ||
page->mapping != NULL ||
page_count(page) != 0 ||
(page->flags & (
@@ -433,7 +433,7 @@ void set_page_refs(struct page *page, in
*/
static void prep_new_page(struct page *page, int order)
{
- if (page->mapping || page_mapped(page) ||
+ if (page->mapping || page_mapcount(page) ||
(page->flags & (
1 << PG_private |
1 << PG_locked |
_