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Subject[PATCH] mm-vmscan-dont-mess-with-pgdat-flags-in-memcg-reclaim-v2-fix
Date
On 04/06/2018 05:13 AM, Shakeel Butt wrote:
> Question: Should this 'flags' be per-node? Is it ok for a congested
> memcg to call wait_iff_congested for all nodes?

Indeed, congestion state should be pre-node. If memcg on node A is
congested, there is no point is stalling memcg reclaim from node B.

Make congestion state per-cgroup-per-node and record it in
'struct mem_cgroup_per_node'.

Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
---
include/linux/memcontrol.h | 5 +++--
mm/vmscan.c | 39 +++++++++++++++++++++++++--------------
2 files changed, 28 insertions(+), 16 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 8b394bbf1c86..af9eed2e3e04 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -120,6 +120,9 @@ struct mem_cgroup_per_node {
unsigned long usage_in_excess;/* Set to the value by which */
/* the soft limit is exceeded*/
bool on_tree;
+ bool congested; /* memcg has many dirty pages */
+ /* backed by a congested BDI */
+
struct mem_cgroup *memcg; /* Back pointer, we cannot */
/* use container_of */
};
@@ -189,8 +192,6 @@ struct mem_cgroup {
/* vmpressure notifications */
struct vmpressure vmpressure;

- unsigned long flags;
-
/*
* Should the accounting and control be hierarchical, per subtree?
*/
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 99688299eba8..78214c899710 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -200,16 +200,27 @@ static bool sane_reclaim(struct scan_control *sc)
return false;
}

-static void set_memcg_bit(enum pgdat_flags flag,
- struct mem_cgroup *memcg)
+static void set_memcg_congestion(pg_data_t *pgdat,
+ struct mem_cgroup *memcg,
+ bool congested)
{
- set_bit(flag, &memcg->flags);
+ struct mem_cgroup_per_node *mz;
+
+ if (!memcg)
+ return;
+
+ mz = mem_cgroup_nodeinfo(memcg, pgdat->node_id);
+ WRITE_ONCE(mz->congested, congested);
}

-static int test_memcg_bit(enum pgdat_flags flag,
+static bool memcg_congested(pg_data_t *pgdat,
struct mem_cgroup *memcg)
{
- return test_bit(flag, &memcg->flags);
+ struct mem_cgroup_per_node *mz;
+
+ mz = mem_cgroup_nodeinfo(memcg, pgdat->node_id);
+ return READ_ONCE(mz->congested);
+
}
#else
static bool global_reclaim(struct scan_control *sc)
@@ -222,15 +233,16 @@ static bool sane_reclaim(struct scan_control *sc)
return true;
}

-static inline void set_memcg_bit(enum pgdat_flags flag,
- struct mem_cgroup *memcg)
+static inline void set_memcg_congestion(struct pglist_data *pgdat,
+ struct mem_cgroup *memcg, bool congested)
{
}

-static inline int test_memcg_bit(enum pgdat_flags flag,
- struct mem_cgroup *memcg)
+static inline bool memcg_congested(struct pglist_data *pgdat,
+ struct mem_cgroup *memcg)
{
- return 0;
+ return false;
+
}
#endif

@@ -2482,7 +2494,7 @@ static inline bool should_continue_reclaim(struct pglist_data *pgdat,
static bool pgdat_memcg_congested(pg_data_t *pgdat, struct mem_cgroup *memcg)
{
return test_bit(PGDAT_CONGESTED, &pgdat->flags) ||
- (memcg && test_memcg_bit(PGDAT_CONGESTED, memcg));
+ (memcg && memcg_congested(pgdat, memcg));
}

static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc)
@@ -2617,7 +2629,7 @@ static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc)
*/
if (!global_reclaim(sc) && sane_reclaim(sc) &&
sc->nr.dirty && sc->nr.dirty == sc->nr.congested)
- set_memcg_bit(PGDAT_CONGESTED, root);
+ set_memcg_congestion(pgdat, root, true);

/*
* Stall direct reclaim for IO completions if underlying BDIs
@@ -2844,6 +2856,7 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
continue;
last_pgdat = zone->zone_pgdat;
snapshot_refaults(sc->target_mem_cgroup, zone->zone_pgdat);
+ set_memcg_congestion(last_pgdat, sc->target_mem_cgroup, false);
}

delayacct_freepages_end();
@@ -3067,7 +3080,6 @@ unsigned long mem_cgroup_shrink_node(struct mem_cgroup *memcg,
* the priority and make it zero.
*/
shrink_node_memcg(pgdat, memcg, &sc, &lru_pages);
- clear_bit(PGDAT_CONGESTED, &memcg->flags);

trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed);

@@ -3113,7 +3125,6 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
noreclaim_flag = memalloc_noreclaim_save();
nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
memalloc_noreclaim_restore(noreclaim_flag);
- clear_bit(PGDAT_CONGESTED, &memcg->flags);

trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);

--
2.16.1
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