2020-03-12 16:42:37

by Chris Down

Subject: [PATCH] mm, memcg: Bypass high reclaim iteration for cgroup hierarchy root

The root of the hierarchy cannot have high set, so we will never reclaim
based on it. This makes that clearer and avoids another entry.

Signed-off-by: Chris Down <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
---
mm/memcontrol.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 63bb6a2aab81..ab9d24a657b9 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2232,7 +2232,8 @@ static void reclaim_high(struct mem_cgroup *memcg,
continue;
memcg_memory_event(memcg, MEMCG_HIGH);
try_to_free_mem_cgroup_pages(memcg, nr_pages, gfp_mask, true);
- } while ((memcg = parent_mem_cgroup(memcg)));
+ } while ((memcg = parent_mem_cgroup(memcg)) &&
+ !mem_cgroup_is_root(memcg));
}

static void high_work_func(struct work_struct *work)
--
2.25.1

2020-04-02 01:23:37

by Andrew Morton

Subject: Re: [PATCH] mm, memcg: Bypass high reclaim iteration for cgroup hierarchy root

On Thu, 12 Mar 2020 16:41:37 +0000 Chris Down <[email protected]> wrote:

> The root of the hierarchy cannot have high set, so we will never reclaim
> based on it. This makes that clearer and avoids another entry.
>
> ...
>
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2232,7 +2232,8 @@ static void reclaim_high(struct mem_cgroup *memcg,
> continue;
> memcg_memory_event(memcg, MEMCG_HIGH);
> try_to_free_mem_cgroup_pages(memcg, nr_pages, gfp_mask, true);
> - } while ((memcg = parent_mem_cgroup(memcg)));
> + } while ((memcg = parent_mem_cgroup(memcg)) &&
> + !mem_cgroup_is_root(memcg));
> }
>
> static void high_work_func(struct work_struct *work)

Does someone have time to review this one?

Thanks.

2020-04-02 16:39:39

by Johannes Weiner

Subject: Re: [PATCH] mm, memcg: Bypass high reclaim iteration for cgroup hierarchy root

On Thu, Mar 12, 2020 at 04:41:37PM +0000, Chris Down wrote:
> The root of the hierarchy cannot have high set, so we will never reclaim
> based on it. This makes that clearer and avoids another entry.
>
> Signed-off-by: Chris Down <[email protected]>
> Cc: Andrew Morton <[email protected]>
> Cc: Johannes Weiner <[email protected]>
> Cc: Tejun Heo <[email protected]>
> Cc: [email protected]
> Cc: [email protected]
> Cc: [email protected]
> Cc: [email protected]

This makes sense, memory.high doesn't exist on the root.

And the mem_cgroup_is_root() check, a simple pointer comparison, is
cheaper than reading the page_counter atomic and memcg->high (which we
already know to be PAGE_COUNTER_MAX).

Acked-by: Johannes Weiner <[email protected]>