* + mm-remove-misleading-alignment-claims.patch added to -mm tree
@ 2017-12-20 23:42 akpm
0 siblings, 0 replies; only message in thread
From: akpm @ 2017-12-20 23:42 UTC (permalink / raw)
To: mawilcox, cl, kirill.shutemov, mhocko, rdunlap, mm-commits
The patch titled
Subject: mm: remove misleading alignment claims
has been added to the -mm tree. Its filename is
mm-remove-misleading-alignment-claims.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-remove-misleading-alignment-claims.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-remove-misleading-alignment-claims.patch
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------------------------------------------------------
From: Matthew Wilcox <mawilcox@microsoft.com>
Subject: mm: remove misleading alignment claims
The "third double word block" isn't on 32-bit systems. The layout looks
like this:
unsigned long flags;
struct address_space *mapping
pgoff_t index;
atomic_t _mapcount;
atomic_t _refcount;
which is 32 bytes on 64-bit, but 20 bytes on 32-bit. Nobody is trying to
use the fact that it's double-word aligned today, so just remove the
misleading claims.
Link: http://lkml.kernel.org/r/20171220155552.15884-4-willy@infradead.org
Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Christoph Lameter <cl@linux.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
include/linux/mm_types.h | 13 +++++--------
1 file changed, 5 insertions(+), 8 deletions(-)
diff -puN include/linux/mm_types.h~mm-remove-misleading-alignment-claims include/linux/mm_types.h
--- a/include/linux/mm_types.h~mm-remove-misleading-alignment-claims
+++ a/include/linux/mm_types.h
@@ -33,11 +33,11 @@ struct hmm;
* a page, though if it is a pagecache page, rmap structures can tell us
* who is mapping it.
*
- * The objects in struct page are organized in double word blocks in
- * order to allows us to use atomic double word operations on portions
- * of struct page. That is currently only used by slub but the arrangement
- * allows the use of atomic double word operations on the flags/mapping
- * and lru list pointers also.
+ * SLUB uses cmpxchg_double() to atomically update its freelist and
+ * counters. That requires that freelist & counters be adjacent and
+ * double-word aligned. We align all struct pages to double-word
+ * boundaries, and ensure that 'freelist' is aligned within the
+ * struct.
*/
#ifdef CONFIG_HAVE_ALIGNED_STRUCT_PAGE
#define _struct_page_alignment __aligned(2 * sizeof(unsigned long))
@@ -113,8 +113,6 @@ struct page {
};
/*
- * Third double word block
- *
* WARNING: bit 0 of the first word encode PageTail(). That means
* the rest users of the storage space MUST NOT use the bit to
* avoid collision and false-positive PageTail().
@@ -175,7 +173,6 @@ struct page {
#endif
};
- /* Remainder is not double word aligned */
union {
unsigned long private; /* Mapping-private opaque data:
* usually used for buffer_heads
_
Patches currently in -mm which might be from mawilcox@microsoft.com are
provide-useful-debugging-information-for-vm_bug.patch
mm-align-struct-page-more-aesthetically.patch
mm-de-indent-struct-page.patch
mm-remove-misleading-alignment-claims.patch
mm-improve-comment-on-page-mapping.patch
mm-introduce-_slub_counter_t.patch
mm-store-compound_dtor-compound_order-as-bytes.patch
mm-document-how-to-use-struct-page.patch
mm-remove-reference-to-pg_buddy.patch
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2017-12-20 23:42 + mm-remove-misleading-alignment-claims.patch added to -mm tree akpm
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