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

[Daisuke Nishimura]

On Wed, 20 Oct 2010 13:18:57 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu at jp.fujitsu.com> wrote:

> 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 ?
> 
It's counted as memcg_hierarchical_free_pages() in mem_cgroup_page_stat().
As for FREEPAGES, we should count ancestors, not children.

mem_cgroup_page_stat():
   1311         if (mem && !mem_cgroup_is_root(mem)) {
   1312                 /*
   1313                  * If we're looking for dirtyable pages we need to evaluate
   1314                  * free pages depending on the limit and usage of the parents
   1315                  * first of all.
   1316                  */
   1317                 if (item == MEMCG_NR_DIRTYABLE_PAGES)
   1318                         value = memcg_hierarchical_free_pages(mem);
   1319                 else
   1320                         value = 0;
   1321                 /*
   1322                  * Recursively evaluate page statistics against all cgroup
   1323                  * under hierarchy tree
   1324                  */
   1325                 for_each_mem_cgroup_tree(iter, mem)
   1326                         value += mem_cgroup_local_page_stat(iter, item);

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