From: KAMEZAWA Hiroyuki Date: Thu, 13 Jan 2011 23:47:38 +0000 (-0800) Subject: memcg: add lock to synchronize page accounting and migration X-Git-Tag: v2.6.38-rc1~79 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=dbd4ea78f002df283c95d9774837041735fa1bf9;p=pandora-kernel.git memcg: add lock to synchronize page accounting and migration Introduce a new bit spin lock, PCG_MOVE_LOCK, to synchronize the page accounting and migration code. This reworks the locking scheme of _update_stat() and _move_account() by adding new lock bit PCG_MOVE_LOCK, which is always taken under IRQ disable. 1. If pages are being migrated from a memcg, then updates to that memcg page statistics are protected by grabbing PCG_MOVE_LOCK using move_lock_page_cgroup(). In an upcoming commit, memcg dirty page accounting will be updating memcg page accounting (specifically: num writeback pages) from IRQ context (softirq). Avoid a deadlocking nested spin lock attempt by disabling irq on the local processor when grabbing the PCG_MOVE_LOCK. 2. lock for update_page_stat is used only for avoiding race with move_account(). So, IRQ awareness of lock_page_cgroup() itself is not a problem. The problem is between mem_cgroup_update_page_stat() and mem_cgroup_move_account_page(). Trade-off: * Changing lock_page_cgroup() to always disable IRQ (or local_bh) has some impacts on performance and I think it's bad to disable IRQ when it's not necessary. * adding a new lock makes move_account() slower. Score is here. Performance Impact: moving a 8G anon process. Before: real 0m0.792s user 0m0.000s sys 0m0.780s After: real 0m0.854s user 0m0.000s sys 0m0.842s This score is bad but planned patches for optimization can reduce this impact. Signed-off-by: KAMEZAWA Hiroyuki Signed-off-by: Greg Thelen Reviewed-by: Minchan Kim Acked-by: Daisuke Nishimura Cc: Andrea Righi Cc: Balbir Singh Cc: Wu Fengguang Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Reading git-diff-tree failed