Messages in this thread | | | Date | Tue, 12 Oct 2010 11:09:35 +0530 | From | Balbir Singh <> | Subject | Re: [PATCH 04/10] memcg: disable local interrupts in lock_page_cgroup() |
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* Greg Thelen <gthelen@google.com> [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@develer.com> > Signed-off-by: Greg Thelen <gthelen@google.com> --
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
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