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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 /include/asm-alpha/parport.h
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 'include/asm-alpha/parport.h')
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