On Fri, Oct 24, 2014 at 02:37:34PM +0400, Vladimir Davydov wrote:
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index a384339bf718..2cf6b04a4e0c 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -339,6 +339,26 @@ shrink_slab_node(struct shrink_control *shrinkctl, struct shrinker *shrinker,
> return freed;
> }
>
> +static unsigned long
> +run_shrinker(struct shrink_control *shrinkctl, struct shrinker *shrinker,
> + unsigned long nr_pages_scanned, unsigned long lru_pages)
> +{
> + unsigned long freed = 0;
> +
> + if (!(shrinker->flags & SHRINKER_NUMA_AWARE)) {
> + shrinkctl->nid = 0;
> + return shrink_slab_node(shrinkctl, shrinker,
> + nr_pages_scanned, lru_pages);
> + }
> +
> + for_each_node_mask(shrinkctl->nid, shrinkctl->nodes_to_scan) {
> + if (node_online(shrinkctl->nid))
> + freed += shrink_slab_node(shrinkctl, shrinker,
> + nr_pages_scanned, lru_pages);
> + }
> + return freed;
> +}
The slab shrinking logic accumulates the lru pages, as well as the
nodes_to_scan mask, when going over the zones, only to go over the
zones here again using the accumulated node information. Why not just
invoke the thing per-zone instead in the first place? Kswapd already
does that (although it could probably work with the per-zone lru_pages
and nr_scanned deltas) and direct reclaim should as well. It would
simplify the existing code as well as your series a lot.
> + /*
> + * For memcg-aware shrinkers iterate over the target memcg
> + * hierarchy and run the shrinker on each kmem-active memcg
> + * found in the hierarchy.
> + */
> + shrinkctl->memcg = shrinkctl->target_mem_cgroup;
> + do {
> + if (!shrinkctl->memcg ||
> + memcg_kmem_is_active(shrinkctl->memcg))
> + freed += run_shrinker(shrinkctl, shrinker,
> nr_pages_scanned, lru_pages);
> -
> - }
> + } while ((shrinkctl->memcg =
> + mem_cgroup_iter(shrinkctl->target_mem_cgroup,
> + shrinkctl->memcg, NULL)) != NULL);
More symptoms of the above. This hierarchy walk is duplicative and
potentially quite expensive.
> @@ -2381,6 +2414,7 @@ static bool shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
> gfp_t orig_mask;
> struct shrink_control shrink = {
> .gfp_mask = sc->gfp_mask,
> + .target_mem_cgroup = sc->target_mem_cgroup,
> };
> enum zone_type requested_highidx = gfp_zone(sc->gfp_mask);
> bool reclaimable = false;
> @@ -2400,18 +2434,22 @@ static bool shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
> gfp_zone(sc->gfp_mask), sc->nodemask) {
> if (!populated_zone(zone))
> continue;
> +
> + if (global_reclaim(sc) &&
> + !cpuset_zone_allowed(zone, GFP_KERNEL | __GFP_HARDWALL))
> + continue;
> +
> + lru_pages += global_reclaim(sc) ?
> + zone_reclaimable_pages(zone) :
> + mem_cgroup_zone_reclaimable_pages(zone,
> + sc->target_mem_cgroup);
> + node_set(zone_to_nid(zone), shrink.nodes_to_scan);
And yet another costly hierarchy walk.
The reclaim code walks zonelists according to a nodemask, and within
each zone it walks lruvecs according to the memcg hierarchy. The
shrinkers are wrong in making up an ad-hoc concept of NUMA nodes that
otherwise does not exist anywhere in the VM. Please integrate them
properly instead of adding more duplication on top.
Thanks
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