path: root/mm
diff options
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
parentb599cbdf1c2d88eac7caed00854ee4eecb119a6b (diff)
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')
1 files changed, 14 insertions, 12 deletions
diff --git a/mm/ksm.c b/mm/ksm.c
index c059ca1c935..0320327b8a6 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -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 */
+ int nid; /* when node of unstable tree */
+ };
struct mm_struct *mm;
unsigned long address; /* + low bits used for flags below */
unsigned int oldchecksum; /* when unstable */
- int nid;
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;
@@ -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);
- /*
- * 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.
+ */
stable_node = stable_tree_insert(kpage);
if (stable_node) {