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Message-ID: <20191022210352.GB24142@tower.DHCP.thefacebook.com>
Date: Tue, 22 Oct 2019 21:03:57 +0000
From: Roman Gushchin <guro@...com>
To: Johannes Weiner <hannes@...xchg.org>
CC: Andrew Morton <akpm@...ux-foundation.org>,
Michal Hocko <mhocko@...e.com>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
"cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Kernel Team <Kernel-team@...com>
Subject: Re: [PATCH 8/8] mm: vmscan: harmonize writeback congestion tracking
for nodes & memcgs
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 <guro@...com>
>
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>
> ---
> 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
>
>
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