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authorHugh Dickins <hughd@google.com>2013-02-22 16:36:06 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2013-02-23 17:50:23 -0800
commitbc56620b493496b8a6962080b644ccc537f4d526 (patch)
tree46f59d3ac15cac32cbb97b8a48cc4dffb539b3f8 /mm/memory.c
parentb599cbdf1c2d88eac7caed00854ee4eecb119a6b (diff)
downloadlinux-bc56620b493496b8a6962080b644ccc537f4d526.tar.gz
ksm: shrink 32-bit rmap_item back to 32 bytes
Think of struct rmap_item as an extension of struct page (restricted to MADV_MERGEABLE areas): there may be a lot of them, we need to keep them small, especially on 32-bit architectures of limited lowmem. Siting "int nid" after "unsigned int checksum" works nicely on 64-bit, making no change to its 64-byte struct rmap_item; but bloats the 32-bit struct rmap_item from (nicely cache-aligned) 32 bytes to 36 bytes, which rounds up to 40 bytes once allocated from slab. We'd better avoid that. Hey, I only just remembered that the anon_vma pointer in struct rmap_item has no purpose until the rmap_item is hung from a stable tree node (which has its own nid field); and rmap_item's nid field no purpose than to say which tree root to tell rb_erase() when unlinking from an unstable tree. Double them up in a union. There's just one place where we set anon_vma early (when we already hold mmap_sem): now we must remove tree_rmap_item from its unstable tree there, before overwriting nid. No need to spatter BUG()s around: we'd be seeing oopses if this were wrong. Signed-off-by: Hugh Dickins <hughd@google.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Petr Holasek <pholasek@redhat.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Izik Eidus <izik.eidus@ravellosystems.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/memory.c')
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