[PATCH v2 04/11] memcg: disable softirq in lock_page_cgroup()
minchan.kim at gmail.com
Sat Oct 16 22:56:20 PDT 2010
On Sat, Oct 16, 2010 at 6:14 AM, Greg Thelen <gthelen at 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:
> CPU 0 CPU 1
> start move
> lock_page_cgroup /* deadlock */
> 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 at develer.com>
> Signed-off-by: Greg Thelen <gthelen at google.com>
> include/linux/page_cgroup.h | 6 ++++++
> 1 files changed, 6 insertions(+), 0 deletions(-)
> diff --git a/include/linux/page_cgroup.h b/include/linux/page_cgroup.h
> index b59c298..0585546 100644
> --- a/include/linux/page_cgroup.h
> +++ b/include/linux/page_cgroup.h
> @@ -3,6 +3,8 @@
> #ifdef CONFIG_CGROUP_MEM_RES_CTLR
> #include <linux/bit_spinlock.h>
> +#include <linux/hardirq.h>
> * Page Cgroup can be considered as an extended mem_map.
> * A page_cgroup page is associated with every page descriptor. The
> @@ -119,12 +121,16 @@ static inline enum zone_type page_cgroup_zid(struct page_cgroup *pc)
> static inline void lock_page_cgroup(struct page_cgroup *pc)
> + /* This routine is only deadlock safe from softirq or lower. */
> + VM_BUG_ON(in_irq());
> + local_bh_disable();
> bit_spin_lock(PCG_LOCK, &pc->flags);
> static inline void unlock_page_cgroup(struct page_cgroup *pc)
> bit_spin_unlock(PCG_LOCK, &pc->flags);
> + local_bh_enable();
> #else /* CONFIG_CGROUP_MEM_RES_CTLR */
Please, see recent Kame's patch.
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