* Greg Thelen <gthelen@xxxxxxxxxx> [2010-10-03 23:57:59]: > If pages are being migrated from a memcg, then updates to that > memcg's page statistics are protected by grabbing a bit spin lock > using lock_page_cgroup(). In an upcoming commit memcg dirty page > accounting will be updating memcg page accounting (specifically: > num writeback pages) from softirq. Avoid a deadlocking nested > spin lock attempt by disabling interrupts on the local processor > when grabbing the page_cgroup bit_spin_lock in lock_page_cgroup(). > This avoids the following deadlock: > statistic > CPU 0 CPU 1 > inc_file_mapped > rcu_read_lock > start move > synchronize_rcu > lock_page_cgroup > softirq > test_clear_page_writeback > mem_cgroup_dec_page_stat(NR_WRITEBACK) > rcu_read_lock > lock_page_cgroup /* deadlock */ > unlock_page_cgroup > rcu_read_unlock > unlock_page_cgroup > rcu_read_unlock > > By disabling interrupts in lock_page_cgroup, nested calls > are avoided. The softirq would be delayed until after inc_file_mapped > enables interrupts when calling unlock_page_cgroup(). > > The normal, fast path, of memcg page stat updates typically > does not need to call lock_page_cgroup(), so this change does > not affect the performance of the common case page accounting. > > Signed-off-by: Andrea Righi <arighi@xxxxxxxxxxx> > Signed-off-by: Greg Thelen <gthelen@xxxxxxxxxx> -- It will take more convincing, all important functions (charge/uncharge use lock_page_cgroup()). I'd like to see the page fault scalability test results. I am not against this patch, just want to see the scalability numbers. Three Cheers, Balbir -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>