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SubjectRe: [PATCH v2 04/11] memcg: disable softirq in lock_page_cgroup()
On Fri, 15 Oct 2010 14:14:32 -0700
Greg Thelen <gthelen@google.com> wrote:

> 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 softirq 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 softirq in lock_page_cgroup, nested calls are avoided.
> The softirq would be delayed until after inc_file_mapped enables
> softirq 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>

I have a patch for this problem.
So, could you reorder patch as

1,2,3,5,6,7,8,9,10,11

I'll post an add-on patch."12"

move_charge performance improbement patches will be posted later.

Thanks,
-Kame



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