[Devel] Re: [PATCH] memory cgroup enhancements take 4 [5/8] add status accounting function for memory cgroup

[Andrew Morton]

On Wed, 31 Oct 2007 19:30:46 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu at jp.fujitsu.com> wrote:

> Add statistics account infrastructure for memory controller.
> All account information is stored per-cpu and caller will not have
> to take lock or use atomic ops.
> This will be used by memory.stat file later.
> 
> CACHE includes swapcache now. I'd like to divide it to
> PAGECACHE and SWAPCACHE later.
> 
> ...
>
> --- devel-2.6.23-mm1.orig/mm/memcontrol.c
> +++ devel-2.6.23-mm1/mm/memcontrol.c
> @@ -35,6 +35,59 @@ struct cgroup_subsys mem_cgroup_subsys;
>  static const int MEM_CGROUP_RECLAIM_RETRIES = 5;
>  
>  /*
> + * Statistics for memory cgroup.
> + */
> +enum mem_cgroup_stat_index {
> +	/*
> +	 * For MEM_CONTAINER_TYPE_ALL, usage = pagecache + rss.
> +	 */
> +	MEM_CGROUP_STAT_CACHE, 	   /* # of pages charged as cache */
> +	MEM_CGROUP_STAT_RSS,	   /* # of pages charged as rss */
> +
> +	MEM_CGROUP_STAT_NSTATS,
> +};
> +
> +struct mem_cgroup_stat_cpu {
> +	s64 count[MEM_CGROUP_STAT_NSTATS];
> +} ____cacheline_aligned_in_smp;
> +
> +struct mem_cgroup_stat {
> +	struct mem_cgroup_stat_cpu cpustat[NR_CPUS];
> +};
> +
> +/*
> + * modifies value with disabling preempt.
> + */
> +static inline void __mem_cgroup_stat_add(struct mem_cgroup_stat *stat,
> +                enum mem_cgroup_stat_index idx, int val)
> +{
> +	int cpu = smp_processor_id();
> +	preempt_disable();
> +	stat->cpustat[cpu].count[idx] += val;
> +	preempt_enable();
> +}

This is clearly doing smp_processor_id() in preemptible code.  (or the
preempt_disable() just isn't needed).  I fixed it up.

Please ensure that you test with all runtime debugging options enabled -
you should have seen a warning here.

> +/*
> + * For accounting under irq disable, no need for increment preempt count.
> + */
> +static inline void __mem_cgroup_stat_add_safe(struct mem_cgroup_stat *stat,
> +		enum mem_cgroup_stat_index idx, int val)
> +{
> +	int cpu = smp_processor_id();
> +	stat->cpustat[cpu].count[idx] += val;
> +}

There's a wild amount of inlining in that file.  Please, just don't do it -
inline is a highly specialised thing and is rarely needed.

When I removed the obviously-wrong inline statements, the size of
mm/memcontrol.o went from 3823 bytes down to 3495.

It also caused this:

mm/memcontrol.c:65: warning: '__mem_cgroup_stat_add' defined but not used

so I guess I'll just remove that.

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