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| author | Matthew Wilcox <mawilcox@microsoft.com> | 2018-01-31 16:18:51 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2018-01-31 17:18:38 -0800 |
| commit | 4cf7c8bfb36f4b4dbc333bf844ea801d089f44f8 (patch) | |
| tree | f31e80c8cca8aefc43a0199d0715f8e953da9dab | |
| parent | ca9c88c781b8e5d837068db6d1ca8e775fb7e154 (diff) | |
| download | linux-4cf7c8bfb36f4b4dbc333bf844ea801d089f44f8.tar.bz2 | |
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>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
| -rw-r--r-- | include/linux/mm_types.h | 13 |
1 files changed, 5 insertions, 8 deletions
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 27973166af28..c2294e6204e8 100644 --- a/include/linux/mm_types.h +++ b/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 |