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SubjectRe: [PATCH 4/6] memcg: simplify mem_cgroup_page_stat()
On Fri, Nov 12, 2010 at 12:40:22PM -0800, Greg Thelen wrote:
> Johannes Weiner <hannes@cmpxchg.org> writes:
>
> > On Tue, Nov 09, 2010 at 01:24:29AM -0800, Greg Thelen wrote:
> >> The cgroup given to mem_cgroup_page_stat() is no allowed to be
> >> NULL or the root cgroup. So there is no need to complicate the code
> >> handling those cases.
> >>
> >> Signed-off-by: Greg Thelen <gthelen@google.com>
> >> ---
> >> mm/memcontrol.c | 48 ++++++++++++++++++++++--------------------------
> >> 1 files changed, 22 insertions(+), 26 deletions(-)
> >>
> >> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> >> index eb621ee..f8df350 100644
> >> --- a/mm/memcontrol.c
> >> +++ b/mm/memcontrol.c
> >> @@ -1364,12 +1364,10 @@ memcg_hierarchical_free_pages(struct mem_cgroup *mem)
> >>
> >> /*
> >> * mem_cgroup_page_stat() - get memory cgroup file cache statistics
> >> - * @mem: optional memory cgroup to query. If NULL, use current task's
> >> - * cgroup.
> >> + * @mem: memory cgroup to query
> >> * @item: memory statistic item exported to the kernel
> >> *
> >> - * Return the accounted statistic value or negative value if current task is
> >> - * root cgroup.
> >> + * Return the accounted statistic value.
> >> */
> >> long mem_cgroup_page_stat(struct mem_cgroup *mem,
> >> enum mem_cgroup_nr_pages_item item)
> >> @@ -1377,29 +1375,27 @@ long mem_cgroup_page_stat(struct mem_cgroup *mem,
> >> struct mem_cgroup *iter;
> >> long value;
> >>
> >> + VM_BUG_ON(!mem);
> >> + VM_BUG_ON(mem_cgroup_is_root(mem));
> >> +
> >> get_online_cpus();
> >> - rcu_read_lock();
> >> - if (!mem)
> >> - mem = mem_cgroup_from_task(current);
> >> - if (__mem_cgroup_has_dirty_limit(mem)) {
> >
> > What about mem->use_hierarchy that is checked in
> > __mem_cgroup_has_dirty_limit()? Is it no longer needed?
>
> It is no longer needed because the callers of mem_cgroup_page_stat()
> call __mem_cgroup_has_dirty_limit(). In the current implementation, if
> use_hierarchy=1 then the cgroup does not have dirty limits, so calls
> into mem_cgroup_page_stat() are avoided. Specifically the callers of
> mem_cgroup_page_stat() are:
>
> 1. mem_cgroup_dirty_info() which calls __mem_cgroup_has_dirty_limit()
> and returns false if use_hierarchy=1.
>
> 2. throttle_vm_writeout() which calls mem_dirty_info() ->
> mem_cgroup_dirty_info() -> __mem_cgroup_has_dirty_limit() will fall
> back to global limits if use_hierarchy=1.

Thanks for the clarification.

Acked-by: Johannes Weiner <hannes@cmpxchg.org>


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