mm: vmscan: split shrink_node() into node part and memcgs part

This function is getting long and unwieldy, split out the memcg bits.

The updated shrink_node() handles the generic (node) reclaim aspects:
  - global vmpressure notifications
  - writeback and congestion throttling
  - reclaim/compaction management
  - kswapd giving up on unreclaimable nodes

It then calls a new shrink_node_memcgs() which handles cgroup specifics:
  - the cgroup tree traversal
  - memory.low considerations
  - per-cgroup slab shrinking callbacks
  - per-cgroup vmpressure notifications

[hannes@cmpxchg.org: rename "root" to "target_memcg", per Roman]
Link: http://lkml.kernel.org/r/20191025143640.GA386981@cmpxchg.org
Link: http://lkml.kernel.org/r/20191022144803.302233-8-hannes@cmpxchg.org
Change-Id: Ibef223d4f49740dc2ab2e86f2b7c1e529a9643e2
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Roman Gushchin <guro@fb.com>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[backport of the commit 0f6a5cff43d3bcd6aa54c9af267737249d02aa21 from mainline]
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 7175dcd..84d84bb 100644 (file)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2726,26 +2726,18 @@ static bool pgdat_memcg_congested(pg_data_t *pgdat, struct mem_cgroup *memcg)
                (memcg && memcg_congested(pgdat, memcg));
 }
 
-static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc)
+static void shrink_node_memcgs(pg_data_t *pgdat, struct scan_control *sc)
 {
-       struct reclaim_state *reclaim_state = current->reclaim_state;
-       struct mem_cgroup *root = sc->target_mem_cgroup;
-       unsigned long nr_reclaimed, nr_scanned;
-       bool reclaimable = false;
+       struct mem_cgroup *target_memcg = sc->target_mem_cgroup;
        struct mem_cgroup *memcg;
-again:
-       memset(&sc->nr, 0, sizeof(sc->nr));
 
-       nr_reclaimed = sc->nr_reclaimed;
-       nr_scanned = sc->nr_scanned;
-
-       memcg = mem_cgroup_iter(root, NULL, NULL);
+       memcg = mem_cgroup_iter(target_memcg, NULL, NULL);
        do {
                struct lruvec *lruvec = mem_cgroup_lruvec(memcg, pgdat);
                unsigned long reclaimed;
                unsigned long scanned;
 
-               switch (mem_cgroup_protected(root, memcg)) {
+               switch (mem_cgroup_protected(target_memcg, memcg)) {
                case MEMCG_PROT_MIN:
                        /*
                         * Hard protection.
@@ -2789,7 +2781,23 @@ again:
                           sc->nr_scanned - scanned,
                           sc->nr_reclaimed - reclaimed);
 
-       } while ((memcg = mem_cgroup_iter(root, memcg, NULL)));
+       } while ((memcg = mem_cgroup_iter(target_memcg, memcg, NULL)));
+}
+
+static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc)
+{
+       struct reclaim_state *reclaim_state = current->reclaim_state;
+       struct mem_cgroup *target_memcg = sc->target_mem_cgroup;
+       unsigned long nr_reclaimed, nr_scanned;
+       bool reclaimable = false;
+
+again:
+       memset(&sc->nr, 0, sizeof(sc->nr));
+
+       nr_reclaimed = sc->nr_reclaimed;
+       nr_scanned = sc->nr_scanned;
+
+       shrink_node_memcgs(pgdat, sc);
 
        if (reclaim_state) {
                sc->nr_reclaimed += reclaim_state->reclaimed_slab;
@@ -2797,7 +2805,7 @@ again:
        }
 
        /* Record the subtree's reclaim efficiency */
-       vmpressure(sc->gfp_mask, sc->target_mem_cgroup, true,
+       vmpressure(sc->gfp_mask, target_memcg, true,
                   sc->nr_scanned - nr_scanned,
                   sc->nr_reclaimed - nr_reclaimed);
 
@@ -2853,7 +2861,7 @@ again:
         */
        if (cgroup_reclaim(sc) && writeback_throttling_sane(sc) &&
            sc->nr.dirty && sc->nr.dirty == sc->nr.congested)
-               set_memcg_congestion(pgdat, root, true);
+               set_memcg_congestion(pgdat, target_memcg, true);
 
        /*
         * Stall direct reclaim for IO completions if underlying BDIs
@@ -2862,7 +2870,8 @@ again:
         * the LRU too quickly.
         */
        if (!sc->hibernation_mode && !current_is_kswapd() &&
-           current_may_throttle() && pgdat_memcg_congested(pgdat, root))
+           current_may_throttle() &&
+           pgdat_memcg_congested(pgdat, target_memcg))
                wait_iff_congested(BLK_RW_ASYNC, HZ/10);
 
        if (should_continue_reclaim(pgdat, sc->nr_reclaimed - nr_reclaimed,