[PATCH 7/8] mm: vmscan: split shrink_node() into node part and memcgs part

[Johannes Weiner]

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

Signed-off-by: Johannes Weiner <han...@cmpxchg.org>
---
 mm/vmscan.c | 28 ++++++++++++++++++----------
 1 file changed, 18 insertions(+), 10 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index db073b40c432..65baa89740dd 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2722,18 +2722,10 @@ 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 *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);
        do {
@@ -2786,6 +2778,22 @@ static bool shrink_node(pg_data_t *pgdat, struct 
scan_control *sc)
                           sc->nr_reclaimed - reclaimed);
 
        } while ((memcg = mem_cgroup_iter(root, 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 *root = 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;
@@ -2793,7 +2801,7 @@ static bool shrink_node(pg_data_t *pgdat, struct 
scan_control *sc)
        }
 
        /* Record the subtree's reclaim efficiency */
-       vmpressure(sc->gfp_mask, sc->target_mem_cgroup, true,
+       vmpressure(sc->gfp_mask, root, true,
                   sc->nr_scanned - nr_scanned,
                   sc->nr_reclaimed - nr_reclaimed);
 
-- 
2.23.0