Re: [PATCH v4] mm/memcg: try harder to decrease [memory,memsw].limit_in_bytes

Michal Hocko
2018-01-11T12:46:29Z

On Thu 11-01-18 15:21:33, Andrey Ryabinin wrote:
>
>
> On 01/11/2018 01:42 PM, Michal Hocko wrote:
> > On Wed 10-01-18 15:43:17, Andrey Ryabinin wrote:
> > [...]
> >> @@ -2506,15 +2480,13 @@ static int mem_cgroup_resize_limit(struct mem_cgroup *memcg,
> >> if (!ret)
> >> break;
> >>
> >> - try_to_free_mem_cgroup_pages(memcg, 1, GFP_KERNEL, !memsw);
> >> -
> >> - curusage = page_counter_read(counter);
> >> - /* Usage is reduced ? */
> >> - if (curusage >= oldusage)
> >> - retry_count--;
> >> - else
> >> - oldusage = curusage;
> >> - } while (retry_count);
> >> + usage = page_counter_read(counter);
> >> + if (!try_to_free_mem_cgroup_pages(memcg, usage - limit,
> >> + GFP_KERNEL, !memsw)) {
> >
> > If the usage drops below limit in the meantime then you get underflow
> > and reclaim the whole memcg. I do not think this is a good idea. This
> > can also lead to over reclaim. Why don't you simply stick with the
> > original SWAP_CLUSTER_MAX (aka 1 for try_to_free_mem_cgroup_pages)?
> >
>
> Because, if new limit is gigabytes bellow the current usage, retrying to set
> new limit after reclaiming only 32 pages seems unreasonable.

Who would do insanity like that?

> @@ -2487,8 +2487,8 @@ static int mem_cgroup_resize_limit(struct mem_cgroup *memcg,
> if (!ret)
> break;
>
> - usage = page_counter_read(counter);
> - if (!try_to_free_mem_cgroup_pages(memcg, usage - limit,
> + nr_pages = max_t(long, 1, page_counter_read(counter) - limit);
> + if (!try_to_free_mem_cgroup_pages(memcg, nr_pages,
> GFP_KERNEL, !memsw)) {
> ret = -EBUSY;
> break;

How does this address the over reclaim concern?
--
Michal Hocko
SUSE Labs