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author | Hugh Dickins <hughd@google.com> | 2013-02-22 16:36:06 -0800 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2013-02-23 17:50:23 -0800 |
commit | bc56620b493496b8a6962080b644ccc537f4d526 (patch) | |
tree | 46f59d3ac15cac32cbb97b8a48cc4dffb539b3f8 /mm | |
parent | b599cbdf1c2d88eac7caed00854ee4eecb119a6b (diff) | |
download | lwn-bc56620b493496b8a6962080b644ccc537f4d526.tar.gz lwn-bc56620b493496b8a6962080b644ccc537f4d526.zip |
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')
-rw-r--r-- | mm/ksm.c | 26 |
1 files changed, 14 insertions, 12 deletions
@@ -150,23 +150,25 @@ struct stable_node { * struct rmap_item - reverse mapping item for virtual addresses * @rmap_list: next rmap_item in mm_slot's singly-linked rmap_list * @anon_vma: pointer to anon_vma for this mm,address, when in stable tree + * @nid: NUMA node id of unstable tree in which linked (may not match page) * @mm: the memory structure this rmap_item is pointing into * @address: the virtual address this rmap_item tracks (+ flags in low bits) * @oldchecksum: previous checksum of the page at that virtual address - * @nid: NUMA node id of unstable tree in which linked (may not match page) * @node: rb node of this rmap_item in the unstable tree * @head: pointer to stable_node heading this list in the stable tree * @hlist: link into hlist of rmap_items hanging off that stable_node */ struct rmap_item { struct rmap_item *rmap_list; - struct anon_vma *anon_vma; /* when stable */ + union { + struct anon_vma *anon_vma; /* when stable */ +#ifdef CONFIG_NUMA + int nid; /* when node of unstable tree */ +#endif + }; struct mm_struct *mm; unsigned long address; /* + low bits used for flags below */ unsigned int oldchecksum; /* when unstable */ -#ifdef CONFIG_NUMA - int nid; -#endif union { struct rb_node node; /* when node of unstable tree */ struct { /* when listed from stable tree */ @@ -1094,6 +1096,9 @@ static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item, if (err) goto out; + /* Unstable nid is in union with stable anon_vma: remove first */ + remove_rmap_item_from_tree(rmap_item); + /* Must get reference to anon_vma while still holding mmap_sem */ rmap_item->anon_vma = vma->anon_vma; get_anon_vma(vma->anon_vma); @@ -1468,14 +1473,11 @@ static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item) kpage = try_to_merge_two_pages(rmap_item, page, tree_rmap_item, tree_page); put_page(tree_page); - /* - * As soon as we merge this page, we want to remove the - * rmap_item of the page we have merged with from the unstable - * tree, and insert it instead as new node in the stable tree. - */ if (kpage) { - remove_rmap_item_from_tree(tree_rmap_item); - + /* + * The pages were successfully merged: insert new + * node in the stable tree and add both rmap_items. + */ lock_page(kpage); stable_node = stable_tree_insert(kpage); if (stable_node) { |