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

KAMEZAWA Hiroyuki
2010-10-20T04:38:56Z

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

> KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> writes:
>
> > On Tue, 19 Oct 2010 10:00:15 +0900
> > KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> >
> >> On Mon, 18 Oct 2010 17:39:44 -0700
> >> Greg Thelen <gthelen@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@develer.com>
> >> > Signed-off-by: Greg Thelen <gthelen@google.com>
> >>
> >> Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@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;
> }