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    Subject[PATCH] cpuset semaphore depth check optimize
    Optimize the deadlock avoidance check on the global cpuset
    semaphore cpuset_sem. Instead of adding a depth counter to the
    task struct of each task, rather just two words are enough, one
    to store the depth and the other the current cpuset_sem holder.

    Thanks to Nikita Danilov for the idea.

    Signed-off-by: Paul Jackson <pj@sgi.com>

    Index: linux-2.6.13-mem_exclusive_oom/include/linux/sched.h
    ===================================================================
    --- linux-2.6.13-mem_exclusive_oom.orig/include/linux/sched.h
    +++ linux-2.6.13-mem_exclusive_oom/include/linux/sched.h
    @@ -765,7 +765,6 @@ struct task_struct {
    short il_next;
    #endif
    #ifdef CONFIG_CPUSETS
    - short cpuset_sem_nest_depth;
    struct cpuset *cpuset;
    nodemask_t mems_allowed;
    int cpuset_mems_generation;
    Index: linux-2.6.13-mem_exclusive_oom/kernel/cpuset.c
    ===================================================================
    --- linux-2.6.13-mem_exclusive_oom.orig/kernel/cpuset.c
    +++ linux-2.6.13-mem_exclusive_oom/kernel/cpuset.c
    @@ -180,6 +180,8 @@ static struct super_block *cpuset_sb = N
    */

    static DECLARE_MUTEX(cpuset_sem);
    +static struct task_struct *cpuset_sem_owner;
    +static int cpuset_sem_depth;

    /*
    * The global cpuset semaphore cpuset_sem can be needed by the
    @@ -200,16 +202,19 @@ static DECLARE_MUTEX(cpuset_sem);

    static inline void cpuset_down(struct semaphore *psem)
    {
    - if (current->cpuset_sem_nest_depth == 0)
    + if (cpuset_sem_owner != current) {
    down(psem);
    - current->cpuset_sem_nest_depth++;
    + cpuset_sem_owner = current;
    + }
    + cpuset_sem_depth++;
    }

    static inline void cpuset_up(struct semaphore *psem)
    {
    - current->cpuset_sem_nest_depth--;
    - if (current->cpuset_sem_nest_depth == 0)
    + if (--cpuset_sem_depth == 0) {
    + cpuset_sem_owner = NULL;
    up(psem);
    + }
    }

    /*
    --
    I won't rest till it's the best ...
    Programmer, Linux Scalability
    Paul Jackson <pj@sgi.com> 1.650.933.1373
    -
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