On Tue, Oct 22, 2019 at 10:48:03AM -0400, Johannes Weiner wrote: > The current writeback congestion tracking has separate flags for > kswapd reclaim (node level) and cgroup limit reclaim (memcg-node > level). This is unnecessarily complicated: the lruvec is an existing > abstraction layer for that node-memcg intersection. > > Introduce lruvec->flags and LRUVEC_CONGESTED. Then track that at the > reclaim root level, which is either the NUMA node for global reclaim, > or the cgroup-node intersection for cgroup reclaim.
Good idea! Reviewed-by: Roman Gushchin <[email protected]> > > Signed-off-by: Johannes Weiner <[email protected]> > --- > include/linux/memcontrol.h | 6 +-- > include/linux/mmzone.h | 11 ++++-- > mm/vmscan.c | 80 ++++++++++++-------------------------- > 3 files changed, 36 insertions(+), 61 deletions(-) > > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h > index 498cea07cbb1..d8ffcf60440c 100644 > --- a/include/linux/memcontrol.h > +++ b/include/linux/memcontrol.h > @@ -133,9 +133,6 @@ 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 */ > }; > @@ -412,6 +409,9 @@ static inline struct lruvec *mem_cgroup_lruvec(struct > mem_cgroup *memcg, > goto out; > } > > + if (!memcg) > + memcg = root_mem_cgroup; > + > mz = mem_cgroup_nodeinfo(memcg, pgdat->node_id); > lruvec = &mz->lruvec; > out: > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > index 449a44171026..c04b4c1f01fa 100644 > --- a/include/linux/mmzone.h > +++ b/include/linux/mmzone.h > @@ -296,6 +296,12 @@ struct zone_reclaim_stat { > unsigned long recent_scanned[2]; > }; > > +enum lruvec_flags { > + LRUVEC_CONGESTED, /* lruvec has many dirty pages > + * backed by a congested BDI > + */ > +}; > + > struct lruvec { > struct list_head lists[NR_LRU_LISTS]; > struct zone_reclaim_stat reclaim_stat; > @@ -303,6 +309,8 @@ struct lruvec { > atomic_long_t inactive_age; > /* Refaults at the time of last reclaim cycle */ > unsigned long refaults; > + /* Various lruvec state flags (enum lruvec_flags) */ > + unsigned long flags; > #ifdef CONFIG_MEMCG > struct pglist_data *pgdat; > #endif > @@ -572,9 +580,6 @@ struct zone { > } ____cacheline_internodealigned_in_smp; > > enum pgdat_flags { > - PGDAT_CONGESTED, /* pgdat has many dirty pages backed by > - * a congested BDI > - */ > PGDAT_DIRTY, /* reclaim scanning has recently found > * many dirty file pages at the tail > * of the LRU. > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 65baa89740dd..3e21166d5198 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -267,29 +267,6 @@ static bool writeback_throttling_sane(struct > scan_control *sc) > #endif > return false; > } > - > -static void set_memcg_congestion(pg_data_t *pgdat, > - struct mem_cgroup *memcg, > - bool congested) > -{ > - struct mem_cgroup_per_node *mn; > - > - if (!memcg) > - return; > - > - mn = mem_cgroup_nodeinfo(memcg, pgdat->node_id); > - WRITE_ONCE(mn->congested, congested); > -} > - > -static bool memcg_congested(pg_data_t *pgdat, > - struct mem_cgroup *memcg) > -{ > - struct mem_cgroup_per_node *mn; > - > - mn = mem_cgroup_nodeinfo(memcg, pgdat->node_id); > - return READ_ONCE(mn->congested); > - > -} > #else > static int prealloc_memcg_shrinker(struct shrinker *shrinker) > { > @@ -309,18 +286,6 @@ static bool writeback_throttling_sane(struct > scan_control *sc) > { > return true; > } > - > -static inline void set_memcg_congestion(struct pglist_data *pgdat, > - struct mem_cgroup *memcg, bool congested) > -{ > -} > - > -static inline bool memcg_congested(struct pglist_data *pgdat, > - struct mem_cgroup *memcg) > -{ > - return false; > - > -} > #endif > > /* > @@ -2716,12 +2681,6 @@ static inline bool should_continue_reclaim(struct > pglist_data *pgdat, > return inactive_lru_pages > pages_for_compaction; > } > > -static bool pgdat_memcg_congested(pg_data_t *pgdat, struct mem_cgroup *memcg) > -{ > - return test_bit(PGDAT_CONGESTED, &pgdat->flags) || > - (memcg && memcg_congested(pgdat, memcg)); > -} > - > static void shrink_node_memcgs(pg_data_t *pgdat, struct scan_control *sc) > { > struct mem_cgroup *root = sc->target_mem_cgroup; > @@ -2785,8 +2744,11 @@ 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; > + struct lruvec *target_lruvec; > bool reclaimable = false; > > + target_lruvec = mem_cgroup_lruvec(sc->target_mem_cgroup, pgdat); > + > again: > memset(&sc->nr, 0, sizeof(sc->nr)); > > @@ -2829,14 +2791,6 @@ static bool shrink_node(pg_data_t *pgdat, struct > scan_control *sc) > if (sc->nr.writeback && sc->nr.writeback == sc->nr.taken) > set_bit(PGDAT_WRITEBACK, &pgdat->flags); > > - /* > - * Tag a node as congested if all the dirty pages > - * scanned were backed by a congested BDI and > - * wait_iff_congested will stall. > - */ > - if (sc->nr.dirty && sc->nr.dirty == sc->nr.congested) > - set_bit(PGDAT_CONGESTED, &pgdat->flags); > - > /* Allow kswapd to start writing pages during reclaim.*/ > if (sc->nr.unqueued_dirty == sc->nr.file_taken) > set_bit(PGDAT_DIRTY, &pgdat->flags); > @@ -2852,12 +2806,17 @@ static bool shrink_node(pg_data_t *pgdat, struct > scan_control *sc) > } > > /* > + * Tag a node/memcg as congested if all the dirty pages > + * scanned were backed by a congested BDI and > + * wait_iff_congested will stall. > + * > * Legacy memcg will stall in page writeback so avoid forcibly > * stalling in wait_iff_congested(). > */ > - if (cgroup_reclaim(sc) && writeback_throttling_sane(sc) && > + if ((current_is_kswapd() || > + (cgroup_reclaim(sc) && writeback_throttling_sane(sc))) && > sc->nr.dirty && sc->nr.dirty == sc->nr.congested) > - set_memcg_congestion(pgdat, root, true); > + set_bit(LRUVEC_CONGESTED, &target_lruvec->flags); > > /* > * Stall direct reclaim for IO completions if underlying BDIs > @@ -2865,8 +2824,9 @@ static bool shrink_node(pg_data_t *pgdat, struct > scan_control *sc) > * starts encountering unqueued dirty pages or cycling through > * the LRU too quickly. > */ > - if (!sc->hibernation_mode && !current_is_kswapd() && > - current_may_throttle() && pgdat_memcg_congested(pgdat, root)) > + if (!current_is_kswapd() && current_may_throttle() && > + !sc->hibernation_mode && > + test_bit(LRUVEC_CONGESTED, &target_lruvec->flags)) > wait_iff_congested(BLK_RW_ASYNC, HZ/10); > > if (should_continue_reclaim(pgdat, sc->nr_reclaimed - nr_reclaimed, > @@ -3080,8 +3040,16 @@ static unsigned long do_try_to_free_pages(struct > zonelist *zonelist, > if (zone->zone_pgdat == last_pgdat) > 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); > + > + if (cgroup_reclaim(sc)) { > + struct lruvec *lruvec; > + > + lruvec = mem_cgroup_lruvec(sc->target_mem_cgroup, > + zone->zone_pgdat); > + clear_bit(LRUVEC_CONGESTED, &lruvec->flags); > + } > } > > delayacct_freepages_end(); > @@ -3461,7 +3429,9 @@ static bool pgdat_balanced(pg_data_t *pgdat, int order, > int classzone_idx) > /* Clear pgdat state for congested, dirty or under writeback. */ > static void clear_pgdat_congested(pg_data_t *pgdat) > { > - clear_bit(PGDAT_CONGESTED, &pgdat->flags); > + struct lruvec *lruvec = mem_cgroup_lruvec(NULL, pgdat); > + > + clear_bit(LRUVEC_CONGESTED, &lruvec->flags); > clear_bit(PGDAT_DIRTY, &pgdat->flags); > clear_bit(PGDAT_WRITEBACK, &pgdat->flags); > } > -- > 2.23.0 > >
