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SubjectRe: [PATCH v6 15/17] mm: Generalize shrink_slab() calls in shrink_node()
On Fri, May 18, 2018 at 11:44:11AM +0300, Kirill Tkhai wrote:
> From: Vladimir Davydov <vdavydov.dev@gmail.com>
>
> The patch makes shrink_slab() be called for root_mem_cgroup
> in the same way as it's called for the rest of cgroups.
> This simplifies the logic and improves the readability.
>
> Signed-off-by: Vladimir Davydov <vdavydov.dev@gmail.com>
> ktkhai: Description written.
> Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
> ---
> mm/vmscan.c | 13 +++----------
> 1 file changed, 3 insertions(+), 10 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 2fbf3b476601..f1d23e2df988 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c

You forgot to patch the comment to shrink_slab(). Please take a closer
look at the diff I sent you:

@@ -486,10 +486,8 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
* @nid is passed along to shrinkers with SHRINKER_NUMA_AWARE set,
* unaware shrinkers will receive a node id of 0 instead.
*
- * @memcg specifies the memory cgroup to target. If it is not NULL,
- * only shrinkers with SHRINKER_MEMCG_AWARE set will be called to scan
- * objects from the memory cgroup specified. Otherwise, only unaware
- * shrinkers are called.
+ * @memcg specifies the memory cgroup to target. Unaware shrinkers
+ * are called only if it is the root cgroup.
*
* @priority is sc->priority, we take the number of objects and >> by priority
* in order to get the scan target.

> @@ -661,9 +661,6 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
> .memcg = memcg,
> };

If you made !MEMCG version of mem_cgroup_is_root return true, as I
suggested in reply to patch 13, you could also simplify the memcg
related check in the beginning of shrink_slab() as in case of
CONFIG_MEMCG 'memcg' is now guaranteed to be != NULL in this function
while in case if !CONFIG_MEMCG mem_cgroup_is_root() would always
return true:

@@ -501,7 +501,7 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
struct shrinker *shrinker;
unsigned long freed = 0;

- if (memcg && !mem_cgroup_is_root(memcg))
+ if (!mem_cgroup_is_root(memcg))
return shrink_slab_memcg(gfp_mask, nid, memcg, priority);

if (!down_read_trylock(&shrinker_rwsem))

>
> - if (!!memcg != !!(shrinker->flags & SHRINKER_MEMCG_AWARE))
> - continue;
> -
> if (!(shrinker->flags & SHRINKER_NUMA_AWARE))
> sc.nid = 0;
>
> @@ -693,6 +690,7 @@ void drop_slab_node(int nid)
> struct mem_cgroup *memcg = NULL;
>
> freed = 0;
> + memcg = mem_cgroup_iter(NULL, NULL, NULL);
> do {
> freed += shrink_slab(GFP_KERNEL, nid, memcg, 0);
> } while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);
> @@ -2712,9 +2710,8 @@ static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc)
> shrink_node_memcg(pgdat, memcg, sc, &lru_pages);
> node_lru_pages += lru_pages;
>
> - if (memcg)
> - shrink_slab(sc->gfp_mask, pgdat->node_id,
> - memcg, sc->priority);
> + shrink_slab(sc->gfp_mask, pgdat->node_id,
> + memcg, sc->priority);
>
> /* Record the group's reclaim efficiency */
> vmpressure(sc->gfp_mask, memcg, false,
> @@ -2738,10 +2735,6 @@ static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc)
> }
> } while ((memcg = mem_cgroup_iter(root, memcg, &reclaim)));
>
> - if (global_reclaim(sc))
> - shrink_slab(sc->gfp_mask, pgdat->node_id, NULL,
> - sc->priority);
> -
> if (reclaim_state) {
> sc->nr_reclaimed += reclaim_state->reclaimed_slab;
> reclaim_state->reclaimed_slab = 0;
>

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