[Devel] Re: [PATCH v3 11/11] memcg: check memcg dirty limits in page writeback

[KAMEZAWA Hiroyuki]

On Tue, 19 Oct 2010 21:33:21 -0700
Greg Thelen <gthelen at google.com> wrote:

> KAMEZAWA Hiroyuki <kamezawa.hiroyu at jp.fujitsu.com> writes:
> 
> > On Tue, 19 Oct 2010 10:00:15 +0900
> > KAMEZAWA Hiroyuki <kamezawa.hiroyu at jp.fujitsu.com> wrote:
> >
> >> On Mon, 18 Oct 2010 17:39:44 -0700
> >> Greg Thelen <gthelen at google.com> wrote:
> >> 
> >> > If the current process is in a non-root memcg, then
> >> > global_dirty_limits() will consider the memcg dirty limit.
> >> > This allows different cgroups to have distinct dirty limits
> >> > which trigger direct and background writeback at different
> >> > levels.
> >> > 
> >> > Signed-off-by: Andrea Righi <arighi at develer.com>
> >> > Signed-off-by: Greg Thelen <gthelen at google.com>
> >> 
> >> Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu at jp.fujitsu.com>
> >> 
> > Why FREEPAGES in memcg is not counted as dirtyable ?
> >
> > Thanks,
> > -Kame
> 
> I think that FREEPAGES is considered dirtyable.  Below I include the
> latest version of the code, which includes an improved version of
> memcg_hierarchical_free_pages().
> 
> Notice that mem_cgroup_page_stat(MEMCG_NR_DIRTYABLE_PAGES) returns the
> sum of:
> 1. compute free pages using memcg_hierarchical_free_pages()
> 2. mem_cgroup_read_stat(mem, LRU_ACTIVE_FILE) +
> 	mem_cgroup_read_stat(mem, LRU_INACTIVE_FILE)
> 3. if (mem_cgroup_can_swap(mem))
>    ret += mem_cgroup_read_stat(mem, LRU_ACTIVE_ANON) +
> 	mem_cgroup_read_stat(mem, LRU_INACTIVE_ANON)
> 
> This algorithm is similar to how global (non-memcg) limits are computed
> in global_dirtyable_memory().
> 

seems very nice. Thank you. 

-Kame

> /*
>  * Return the number of the number of pages that the @mem cgroup could allocate.
>  * If use_hierarchy is set, then this involves parent mem cgroups to find the
>  * cgroup with the smallest free space.
>  */
> static unsigned long long
> memcg_hierarchical_free_pages(struct mem_cgroup *mem)
> {
> 	unsigned long free, min_free;
> 
> 	min_free = global_page_state(NR_FREE_PAGES) << PAGE_SHIFT;
> 
>  	while (mem) {
>  		free = res_counter_read_u64(&mem->res, RES_LIMIT) -
>  			res_counter_read_u64(&mem->res, RES_USAGE);
>  		min_free = min(min_free, free);
>  		mem = parent_mem_cgroup(mem);
>  	}
> 
>  	/* Translate free memory in pages */
>  	return min_free >> PAGE_SHIFT;
> }
> 
> /*
>  * mem_cgroup_page_stat() - get memory cgroup file cache statistics
>  * @item:      memory statistic item exported to the kernel
>  *
>  * Return the accounted statistic value.
>  */
> s64 mem_cgroup_page_stat(enum mem_cgroup_nr_pages_item item)
> {
> 	struct mem_cgroup *mem;
> 	struct mem_cgroup *iter;
> 	s64 value;
> 
> 	get_online_cpus();
> 	rcu_read_lock();
> 	mem = mem_cgroup_from_task(current);
> 	if (mem && !mem_cgroup_is_root(mem)) {
> 		/*
> 		 * If we're looking for dirtyable pages we need to evaluate
> 		 * free pages depending on the limit and usage of the parents
> 		 * first of all.
> 		 */
> 		if (item == MEMCG_NR_DIRTYABLE_PAGES)
> 			value = memcg_hierarchical_free_pages(mem);
> 		else
> 			value = 0;
> 		/*
> 		 * Recursively evaluate page statistics against all cgroup
> 		 * under hierarchy tree
> 		 */
> 		for_each_mem_cgroup_tree(iter, mem)
> 			value += mem_cgroup_local_page_stat(iter, item);
> 	} else
> 		value = -EINVAL;
> 	rcu_read_unlock();
> 	put_online_cpus();
> 
> 	return value;
> }
> 

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