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Date: Tue, 14 Jan 2014 10:01:08 -0800
From: Dave Hansen <dave@...1.net>
To: linux-mm@...ck.org
Cc: linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
penberg@...nel.org, cl@...ux-foundation.org,
Dave Hansen <dave@...1.net>
Subject: [RFC][PATCH 9/9] mm: fix alignment checks on 32-bit
The checks fail on 32-bit. This needs to get folded back in to
the original patches. Please ignore this for now.
---
b/include/linux/mm_types.h | 14 ++++++++------
b/mm/slab_common.c | 16 ++++++----------
2 files changed, 14 insertions(+), 16 deletions(-)
diff -puN include/linux/mm_types.h~fix-slub-size-32-bit include/linux/mm_types.h
--- a/include/linux/mm_types.h~fix-slub-size-32-bit 2014-01-14 09:57:58.738740304 -0800
+++ b/include/linux/mm_types.h 2014-01-14 09:57:58.743740528 -0800
@@ -37,19 +37,21 @@ struct slub_data {
* slab_lock but _count is not.
*/
struct {
- /* counters is just a helperfor the above bitfield */
+ /* counters is just a helper for the above bitfield */
unsigned long counters;
- atomic_t padding;
+ atomic_t mapcount_padding;
atomic_t separate_count;
};
/*
- * the double-cmpxchg case:
- * counters and _count overlap
+ * the double-cmpxchg case (never used on 32-bit):
+ * counters overlaps _count, and we are careful
+ * to only use 32-bits of 'counters' so that we
+ * do not interfere with _count.
*/
union {
unsigned long counters2;
struct {
- atomic_t padding2;
+ atomic_t _unused_mapcount;
atomic_t _count;
};
};
@@ -73,7 +75,6 @@ struct page {
* updated asynchronously */
union {
struct /* the normal uses */ {
- pgoff_t index; /* Our offset within mapping. */
/*
* mapping: If low bit clear, points to
* inode address_space, or NULL. If page
@@ -82,6 +83,7 @@ struct page {
* see PAGE_MAPPING_ANON below.
*/
struct address_space *mapping;
+ pgoff_t index; /* Our offset within mapping. */
/*
* Count of ptes mapped in mms, to show when page
* is mapped & limit reverse map searches.
diff -puN mm/slab_common.c~fix-slub-size-32-bit mm/slab_common.c
--- a/mm/slab_common.c~fix-slub-size-32-bit 2014-01-14 09:57:58.739740349 -0800
+++ b/mm/slab_common.c 2014-01-14 09:57:58.743740528 -0800
@@ -695,15 +695,11 @@ void slab_build_checks(void)
SLAB_PAGE_CHECK(_count, dontuse_slob_count);
/*
- * When doing a double-cmpxchg, the slub code sucks in
- * _count. But, this is harmless since if _count is
- * modified, the cmpxchg will fail. When not using a
- * real cmpxchg, the slub code uses a lock. But, _count
- * is not modified under that lock and updates can be
- * lost if they race with one of the "faked" cmpxchg
- * under that lock. This makes sure that the space we
- * carve out for _count in that case actually lines up
- * with the real _count.
+ * The slub code uses page->_mapcount's space for some
+ * internal counters. But, since ->_count and
+ * ->_mapcount are 32-bit everywhere and the slub
+ * counters are an unsigned long which changes size,
+ * we need to change the checks on 32 vs. 64-bit.
*/
SLAB_PAGE_CHECK(_count, slub_data.separate_count);
@@ -711,6 +707,6 @@ void slab_build_checks(void)
* We need at least three double-words worth of space to
* ensure that we can align to a double-wordk internally.
*/
- BUILD_BUG_ON(sizeof(struct slub_data) != sizeof(unsigned long) * 3);
+ BUILD_BUG_ON(sizeof(struct slub_data) < sizeof(unsigned long) * 3);
}
_
--
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