Re: [v2 PATCH 8/9] mm: memcontrol: reparent nr_deferred when memcg offline

Dave Chinner
2020-12-15T03:08:02Z

On Mon, Dec 14, 2020 at 02:37:21PM -0800, Yang Shi wrote:
> Now shrinker's nr_deferred is per memcg for memcg aware shrinkers, add to parent's
> corresponding nr_deferred when memcg offline.
>
> Signed-off-by: Yang Shi <shy828301@gmail.com>
> ---
> include/linux/shrinker.h | 4 ++++
> mm/memcontrol.c | 24 ++++++++++++++++++++++++
> mm/vmscan.c | 2 +-
> 3 files changed, 29 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
> index 1eac79ce57d4..85cfc910dde4 100644
> --- a/include/linux/shrinker.h
> +++ b/include/linux/shrinker.h
> @@ -78,6 +78,10 @@ struct shrinker {
> };
> #define DEFAULT_SEEKS 2 /* A good number if you don't know better. */
>
> +#ifdef CONFIG_MEMCG
> +extern int shrinker_nr_max;
> +#endif
> +
> /* Flags */
> #define SHRINKER_REGISTERED (1 << 0)
> #define SHRINKER_NUMA_AWARE (1 << 1)
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 321d1818ce3d..1f191a15bee1 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -59,6 +59,7 @@
> #include <linux/tracehook.h>
> #include <linux/psi.h>
> #include <linux/seq_buf.h>
> +#include <linux/shrinker.h>
> #include "internal.h"
> #include <net/sock.h>
> #include <net/ip.h>
> @@ -612,6 +613,28 @@ void memcg_set_shrinker_bit(struct mem_cgroup *memcg, int nid, int shrinker_id)
> }
> }
>
> +static void memcg_reparent_shrinker_deferred(struct mem_cgroup *memcg)
> +{
> + int i, nid;
> + long nr;
> + struct mem_cgroup *parent;
> + struct memcg_shrinker_deferred *child_deferred, *parent_deferred;
> +
> + parent = parent_mem_cgroup(memcg);
> + if (!parent)
> + parent = root_mem_cgroup;
> +
> + for_each_node(nid) {
> + child_deferred = memcg->nodeinfo[nid]->shrinker_deferred;
> + parent_deferred = parent->nodeinfo[nid]->shrinker_deferred;
> + for (i = 0; i < shrinker_nr_max; i ++) {
> + nr = atomic_long_read(&child_deferred->nr_deferred[i]);
> + atomic_long_add(nr,
> + &parent_deferred->nr_deferred[i]);
> + }
> + }
> +}

I would place this function in vmscan.c alongside the
shrink_slab_set_nr_deferred_memcg() function so that all the
accounting is in the one place.

> +
> /**
> * mem_cgroup_css_from_page - css of the memcg associated with a page
> * @page: page of interest
> @@ -5543,6 +5566,7 @@ static void mem_cgroup_css_offline(struct cgroup_subsys_state *css)
> page_counter_set_low(&memcg->memory, 0);
>
> memcg_offline_kmem(memcg);
> + memcg_reparent_shrinker_deferred(memcg);
> wb_memcg_offline(memcg);
>
> drain_all_stock(memcg);
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 8d5bfd818acd..693a41e89969 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -201,7 +201,7 @@ DECLARE_RWSEM(shrinker_rwsem);
> #define SHRINKER_REGISTERING ((struct shrinker *)~0UL)
>
> static DEFINE_IDR(shrinker_idr);
> -static int shrinker_nr_max;
> +int shrinker_nr_max;

Then we don't need to make yet another variable global...

Cheers,

Dave.
--
Dave Chinner
david@fromorbit.com