On Tue, Jul 04, 2017 at 08:33:38AM -0400, josef@xxxxxxxxxxxxxx wrote:
> From: Josef Bacik <jbacik@xxxxxx>
>
> Following patches will greatly increase our aggressiveness in slab
> reclaim, so we need checks in place to make sure we stop trying to
> reclaim slab once we've hit our reclaim target.
>
> Signed-off-by: Josef Bacik <jbacik@xxxxxx>
> ---
> v1->v2:
> - Don't bail out in shrink_slab() so that we always scan at least batch_size
> objects of every slab regardless of wether we've hit our target or not.
It's no different with v1 for aging fairness POV.
Imagine you have 3 shrinkers in shrinker_list and A has a lots of objects.
HEAD-> A -> B -> C
shrink_slab does scan/reclaims from A srhinker a lot until it meets
sc->nr_to_reclaim. Then, VM does aging B and C with batch_size which is
rather small. It breaks fairness.
In next memory pressure, it shrinks A a lot again but B and C
a little bit.
>
> mm/vmscan.c | 33 ++++++++++++++++++++++-----------
> 1 file changed, 22 insertions(+), 11 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index cf23de9..78860a6 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -305,11 +305,13 @@ EXPORT_SYMBOL(unregister_shrinker);
>
> #define SHRINK_BATCH 128
>
> -static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
> +static unsigned long do_shrink_slab(struct scan_control *sc,
> + struct shrink_control *shrinkctl,
> struct shrinker *shrinker,
> unsigned long nr_scanned,
> unsigned long nr_eligible)
> {
> + struct reclaim_state *reclaim_state = current->reclaim_state;
> unsigned long freed = 0;
> unsigned long long delta;
> long total_scan;
> @@ -394,14 +396,18 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
>
> shrinkctl->nr_to_scan = nr_to_scan;
> ret = shrinker->scan_objects(shrinker, shrinkctl);
> + if (reclaim_state) {
> + sc->nr_reclaimed += reclaim_state->reclaimed_slab;
> + reclaim_state->reclaimed_slab = 0;
> + }
> if (ret == SHRINK_STOP)
> break;
> freed += ret;
> -
> count_vm_events(SLABS_SCANNED, nr_to_scan);
> total_scan -= nr_to_scan;
> scanned += nr_to_scan;
> -
> + if (sc->nr_reclaimed >= sc->nr_to_reclaim)
> + break;
> cond_resched();
> }
>
> @@ -452,7 +458,7 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
> *
> * Returns the number of reclaimed slab objects.
> */
> -static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
> +static unsigned long shrink_slab(struct scan_control *sc, int nid,
> struct mem_cgroup *memcg,
> unsigned long nr_scanned,
> unsigned long nr_eligible)
> @@ -478,8 +484,8 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
> }
>
> list_for_each_entry(shrinker, &shrinker_list, list) {
> - struct shrink_control sc = {
> - .gfp_mask = gfp_mask,
> + struct shrink_control shrinkctl = {
> + .gfp_mask = sc->gfp_mask,
> .nid = nid,
> .memcg = memcg,
> };
> @@ -494,9 +500,10 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
> continue;
>
> if (!(shrinker->flags & SHRINKER_NUMA_AWARE))
> - sc.nid = 0;
> + shrinkctl.nid = 0;
>
> - freed += do_shrink_slab(&sc, shrinker, nr_scanned, nr_eligible);
> + freed += do_shrink_slab(sc, &shrinkctl, shrinker, nr_scanned,
> + nr_eligible);
> }
>
> up_read(&shrinker_rwsem);
> @@ -510,11 +517,15 @@ void drop_slab_node(int nid)
> unsigned long freed;
>
> do {
> + struct scan_control sc = {
> + .nr_to_reclaim = -1UL,
> + .gfp_mask = GFP_KERNEL,
> + };
> struct mem_cgroup *memcg = NULL;
>
> freed = 0;
> do {
> - freed += shrink_slab(GFP_KERNEL, nid, memcg,
> + freed += shrink_slab(&sc, nid, memcg,
> 1000, 1000);
> } while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);
> } while (freed > 10);
> @@ -2600,7 +2611,7 @@ static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc)
> node_lru_pages += lru_pages;
>
> if (memcg)
> - shrink_slab(sc->gfp_mask, pgdat->node_id,
> + shrink_slab(sc, pgdat->node_id,
> memcg, sc->nr_scanned - scanned,
> lru_pages);
>
> @@ -2631,7 +2642,7 @@ static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc)
> * the eligible LRU pages were scanned.
> */
> if (global_reclaim(sc))
> - shrink_slab(sc->gfp_mask, pgdat->node_id, NULL,
> + shrink_slab(sc, pgdat->node_id, NULL,
> sc->nr_scanned - nr_scanned,
> node_lru_pages);
>
> --
> 2.7.4
>
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