Re: [PATCH v2 next] memcg: fix deadlock by avoiding stat lock when anon
From: Johannes Weiner <hannes@cmpxchg.org>
Date: 2012-03-01 10:00:49
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On Wed, Feb 29, 2012 at 06:44:59PM -0800, Hugh Dickins wrote:
Fix deadlock in "memcg: use new logic for page stat accounting". page_remove_rmap() first calls mem_cgroup_begin_update_page_stat(), which may take move_lock_mem_cgroup(), unlocked at the end of page_remove_rmap() by mem_cgroup_end_update_page_stat(). The PageAnon case never needs to mem_cgroup_dec_page_stat(page, MEMCG_NR_FILE_MAPPED); but it often needs to mem_cgroup_uncharge_page(), which does lock_page_cgroup(), while holding that move_lock_mem_cgroup(). Whereas mem_cgroup_move_account() calls move_lock_mem_cgroup() while holding lock_page_cgroup(). Since mem_cgroup_begin and end are unnecessary here for PageAnon, simply avoid the deadlock and wasted calls in that case. Signed-off-by: Hugh Dickins <hughd@google.com>
Agreed, let's keep that lock ordering for now, and the comment makes it clear. Thanks! Acked-by: Johannes Weiner <hannes@cmpxchg.org> -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>