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authorHugh Dickins <hugh@veritas.com>2005-06-21 20:15:12 -0400
committerLinus Torvalds <torvalds@ppc970.osdl.org>2005-06-21 21:46:21 -0400
commitc475a8ab625d567eacf5e30ec35d6d8704558062 (patch)
tree0971bef7b876f1b3eb160621fc2b61cb5313827b /mm/memory.c
parentd296e9cd02c92e576ecce5344026a4df4353cdb2 (diff)
[PATCH] can_share_swap_page: use page_mapcount
Remember that ironic get_user_pages race? when the raised page_count on a page swapped out led do_wp_page to decide that it had to copy on write, so substituted a different page into userspace. 2.6.7 onwards have Andrea's solution, where try_to_unmap_one backs out if it finds page_count raised. Which works, but is unsatisfying (rmap.c has no other page_count heuristics), and was found a few months ago to hang an intensive page migration test. A year ago I was hesitant to engage page_mapcount, now it seems the right fix. So remove the page_count hack from try_to_unmap_one; and use activate_page in unuse_mm when dropping lock, to replace its secondary effect of helping swapoff to make progress in that case. Simplify can_share_swap_page (now called only on anonymous pages) to check page_mapcount + page_swapcount == 1: still needs the page lock to stabilize their (pessimistic) sum, but does not need swapper_space.tree_lock for that. In do_swap_page, move swap_free and unlock_page below page_add_anon_rmap, to keep sum on the high side, and correct when can_share_swap_page called. Signed-off-by: Hugh Dickins <hugh@veritas.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'mm/memory.c')
-rw-r--r--mm/memory.c10
1 files changed, 5 insertions, 5 deletions
diff --git a/mm/memory.c b/mm/memory.c
index 1c0a3db78a05..da91b7bf9986 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1686,10 +1686,6 @@ static int do_swap_page(struct mm_struct * mm,
1686 } 1686 }
1687 1687
1688 /* The page isn't present yet, go ahead with the fault. */ 1688 /* The page isn't present yet, go ahead with the fault. */
1689
1690 swap_free(entry);
1691 if (vm_swap_full())
1692 remove_exclusive_swap_page(page);
1693 1689
1694 inc_mm_counter(mm, rss); 1690 inc_mm_counter(mm, rss);
1695 pte = mk_pte(page, vma->vm_page_prot); 1691 pte = mk_pte(page, vma->vm_page_prot);
@@ -1697,12 +1693,16 @@ static int do_swap_page(struct mm_struct * mm,
1697 pte = maybe_mkwrite(pte_mkdirty(pte), vma); 1693 pte = maybe_mkwrite(pte_mkdirty(pte), vma);
1698 write_access = 0; 1694 write_access = 0;
1699 } 1695 }
1700 unlock_page(page);
1701 1696
1702 flush_icache_page(vma, page); 1697 flush_icache_page(vma, page);
1703 set_pte_at(mm, address, page_table, pte); 1698 set_pte_at(mm, address, page_table, pte);
1704 page_add_anon_rmap(page, vma, address); 1699 page_add_anon_rmap(page, vma, address);
1705 1700
1701 swap_free(entry);
1702 if (vm_swap_full())
1703 remove_exclusive_swap_page(page);
1704 unlock_page(page);
1705
1706 if (write_access) { 1706 if (write_access) {
1707 if (do_wp_page(mm, vma, address, 1707 if (do_wp_page(mm, vma, address,
1708 page_table, pmd, pte) == VM_FAULT_OOM) 1708 page_table, pmd, pte) == VM_FAULT_OOM)