lru_lock needs to be held to update the zone_reclaim_stat statistics. Similar to the previous patch, this requirement again arises fairly naturally because callers are holding lru_lock already.
In preparation for allowing concurrent adds and removes from the LRU, however, make concurrent updates to these statistics safe without lru_lock. The lock continues to be held until later in the series, when it is replaced with a rwlock that also disables preemption, maintaining the assumption in the comment above __update_page_reclaim_stat, which is introduced here. Use a combination of per-cpu counters and atomics. Signed-off-by: Daniel Jordan <[email protected]> --- include/linux/mmzone.h | 50 ++++++++++++++++++++++++++++++++++++++++++ init/main.c | 1 + mm/memcontrol.c | 20 ++++++++--------- mm/memory_hotplug.c | 1 + mm/mmzone.c | 14 ++++++++++++ mm/swap.c | 14 ++++++++---- mm/vmscan.c | 42 ++++++++++++++++++++--------------- 7 files changed, 110 insertions(+), 32 deletions(-) diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index 32699b2dc52a..6d4c23a3069d 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -229,6 +229,12 @@ struct zone_reclaim_stat { * * The anon LRU stats live in [0], file LRU stats in [1] */ + atomic_long_t recent_rotated[2]; + atomic_long_t recent_scanned[2]; +}; + +/* These spill into the counters in struct zone_reclaim_stat beyond a cutoff. */ +struct zone_reclaim_stat_cpu { unsigned long recent_rotated[2]; unsigned long recent_scanned[2]; }; @@ -236,6 +242,7 @@ struct zone_reclaim_stat { struct lruvec { struct list_head lists[NR_LRU_LISTS]; struct zone_reclaim_stat reclaim_stat; + struct zone_reclaim_stat_cpu __percpu *reclaim_stat_cpu; /* Evictions & activations on the inactive file list */ atomic_long_t inactive_age; /* Refaults at the time of last reclaim cycle */ @@ -245,6 +252,47 @@ struct lruvec { #endif }; +#define RECLAIM_STAT_BATCH 32U /* From SWAP_CLUSTER_MAX */ + +/* + * Callers of the below three functions that update reclaim stats must hold + * lru_lock and have preemption disabled. Use percpu counters that spill into + * atomics to allow concurrent updates when multiple readers hold lru_lock. + */ + +static inline void __update_page_reclaim_stat(unsigned long count, + unsigned long *percpu_stat, + atomic_long_t *stat) +{ + unsigned long val = *percpu_stat + count; + + if (unlikely(val > RECLAIM_STAT_BATCH)) { + atomic_long_add(val, stat); + val = 0; + } + *percpu_stat = val; +} + +static inline void update_reclaim_stat_scanned(struct lruvec *lruvec, int file, + unsigned long count) +{ + struct zone_reclaim_stat_cpu __percpu *percpu_stat = + this_cpu_ptr(lruvec->reclaim_stat_cpu); + + __update_page_reclaim_stat(count, &percpu_stat->recent_scanned[file], + &lruvec->reclaim_stat.recent_scanned[file]); +} + +static inline void update_reclaim_stat_rotated(struct lruvec *lruvec, int file, + unsigned long count) +{ + struct zone_reclaim_stat_cpu __percpu *percpu_stat = + this_cpu_ptr(lruvec->reclaim_stat_cpu); + + __update_page_reclaim_stat(count, &percpu_stat->recent_rotated[file], + &lruvec->reclaim_stat.recent_rotated[file]); +} + /* Mask used at gathering information at once (see memcontrol.c) */ #define LRU_ALL_FILE (BIT(LRU_INACTIVE_FILE) | BIT(LRU_ACTIVE_FILE)) #define LRU_ALL_ANON (BIT(LRU_INACTIVE_ANON) | BIT(LRU_ACTIVE_ANON)) @@ -795,6 +843,8 @@ extern void init_currently_empty_zone(struct zone *zone, unsigned long start_pfn unsigned long size); extern void lruvec_init(struct lruvec *lruvec); +extern void lruvec_init_late(struct lruvec *lruvec); +extern void lruvecs_init_late(void); static inline struct pglist_data *lruvec_pgdat(struct lruvec *lruvec) { diff --git a/init/main.c b/init/main.c index 3b4ada11ed52..80ad02fe99de 100644 --- a/init/main.c +++ b/init/main.c @@ -526,6 +526,7 @@ static void __init mm_init(void) init_espfix_bsp(); /* Should be run after espfix64 is set up. */ pti_init(); + lruvecs_init_late(); } asmlinkage __visible void __init start_kernel(void) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 5463ad160e10..f7f9682482cd 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -3152,22 +3152,22 @@ static int memcg_stat_show(struct seq_file *m, void *v) pg_data_t *pgdat; struct mem_cgroup_per_node *mz; struct zone_reclaim_stat *rstat; - unsigned long recent_rotated[2] = {0, 0}; - unsigned long recent_scanned[2] = {0, 0}; + unsigned long rota[2] = {0, 0}; + unsigned long scan[2] = {0, 0}; for_each_online_pgdat(pgdat) { mz = mem_cgroup_nodeinfo(memcg, pgdat->node_id); rstat = &mz->lruvec.reclaim_stat; - recent_rotated[0] += rstat->recent_rotated[0]; - recent_rotated[1] += rstat->recent_rotated[1]; - recent_scanned[0] += rstat->recent_scanned[0]; - recent_scanned[1] += rstat->recent_scanned[1]; + rota[0] += atomic_long_read(&rstat->recent_rotated[0]); + rota[1] += atomic_long_read(&rstat->recent_rotated[1]); + scan[0] += atomic_long_read(&rstat->recent_scanned[0]); + scan[1] += atomic_long_read(&rstat->recent_scanned[1]); } - seq_printf(m, "recent_rotated_anon %lu\n", recent_rotated[0]); - seq_printf(m, "recent_rotated_file %lu\n", recent_rotated[1]); - seq_printf(m, "recent_scanned_anon %lu\n", recent_scanned[0]); - seq_printf(m, "recent_scanned_file %lu\n", recent_scanned[1]); + seq_printf(m, "recent_rotated_anon %lu\n", rota[0]); + seq_printf(m, "recent_rotated_file %lu\n", rota[1]); + seq_printf(m, "recent_scanned_anon %lu\n", scan[0]); + seq_printf(m, "recent_scanned_file %lu\n", scan[1]); } #endif diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c index 25982467800b..d3ebb11c3f9f 100644 --- a/mm/memory_hotplug.c +++ b/mm/memory_hotplug.c @@ -1009,6 +1009,7 @@ static pg_data_t __ref *hotadd_new_pgdat(int nid, u64 start) /* init node's zones as empty zones, we don't have any present pages.*/ free_area_init_node(nid, zones_size, start_pfn, zholes_size); pgdat->per_cpu_nodestats = alloc_percpu(struct per_cpu_nodestat); + lruvec_init_late(node_lruvec(pgdat)); /* * The node we allocated has no zone fallback lists. For avoiding diff --git a/mm/mmzone.c b/mm/mmzone.c index 4686fdc23bb9..090cd4f7effb 100644 --- a/mm/mmzone.c +++ b/mm/mmzone.c @@ -9,6 +9,7 @@ #include <linux/stddef.h> #include <linux/mm.h> #include <linux/mmzone.h> +#include <linux/percpu.h> struct pglist_data *first_online_pgdat(void) { @@ -96,6 +97,19 @@ void lruvec_init(struct lruvec *lruvec) INIT_LIST_HEAD(&lruvec->lists[lru]); } +void lruvec_init_late(struct lruvec *lruvec) +{ + lruvec->reclaim_stat_cpu = alloc_percpu(struct zone_reclaim_stat_cpu); +} + +void lruvecs_init_late(void) +{ + pg_data_t *pgdat; + + for_each_online_pgdat(pgdat) + lruvec_init_late(node_lruvec(pgdat)); +} + #if defined(CONFIG_NUMA_BALANCING) && !defined(LAST_CPUPID_NOT_IN_PAGE_FLAGS) int page_cpupid_xchg_last(struct page *page, int cpupid) { diff --git a/mm/swap.c b/mm/swap.c index 3dd518832096..219c234d632f 100644 --- a/mm/swap.c +++ b/mm/swap.c @@ -34,6 +34,7 @@ #include <linux/uio.h> #include <linux/hugetlb.h> #include <linux/page_idle.h> +#include <linux/mmzone.h> #include "internal.h" @@ -260,14 +261,19 @@ void rotate_reclaimable_page(struct page *page) } } +/* + * Updates page reclaim statistics using per-cpu counters that spill into + * atomics above a threshold. + * + * Assumes that the caller has disabled preemption. IRQs may be enabled + * because this function is not called from irq context. + */ static void update_page_reclaim_stat(struct lruvec *lruvec, int file, int rotated) { - struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat; - - reclaim_stat->recent_scanned[file]++; + update_reclaim_stat_scanned(lruvec, file, 1); if (rotated) - reclaim_stat->recent_rotated[file]++; + update_reclaim_stat_rotated(lruvec, file, 1); } static void __activate_page(struct page *page, struct lruvec *lruvec, diff --git a/mm/vmscan.c b/mm/vmscan.c index 9270a4370d54..730b6d0c6c61 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1655,7 +1655,6 @@ static int too_many_isolated(struct pglist_data *pgdat, int file, static noinline_for_stack void putback_inactive_pages(struct lruvec *lruvec, struct list_head *page_list) { - struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat; struct pglist_data *pgdat = lruvec_pgdat(lruvec); LIST_HEAD(pages_to_free); @@ -1684,7 +1683,7 @@ putback_inactive_pages(struct lruvec *lruvec, struct list_head *page_list) if (is_active_lru(lru)) { int file = is_file_lru(lru); int numpages = hpage_nr_pages(page); - reclaim_stat->recent_rotated[file] += numpages; + update_reclaim_stat_rotated(lruvec, file, numpages); } if (put_page_testzero(page)) { __ClearPageLRU(page); @@ -1736,7 +1735,6 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec, isolate_mode_t isolate_mode = 0; int file = is_file_lru(lru); struct pglist_data *pgdat = lruvec_pgdat(lruvec); - struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat; bool stalled = false; while (unlikely(too_many_isolated(pgdat, file, sc))) { @@ -1763,7 +1761,7 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec, &nr_scanned, sc, isolate_mode, lru); __mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, nr_taken); - reclaim_stat->recent_scanned[file] += nr_taken; + update_reclaim_stat_scanned(lruvec, file, nr_taken); if (current_is_kswapd()) { if (global_reclaim(sc)) @@ -1914,7 +1912,6 @@ static void shrink_active_list(unsigned long nr_to_scan, LIST_HEAD(l_active); LIST_HEAD(l_inactive); struct page *page; - struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat; unsigned nr_deactivate, nr_activate; unsigned nr_rotated = 0; isolate_mode_t isolate_mode = 0; @@ -1932,7 +1929,7 @@ static void shrink_active_list(unsigned long nr_to_scan, &nr_scanned, sc, isolate_mode, lru); __mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, nr_taken); - reclaim_stat->recent_scanned[file] += nr_taken; + update_reclaim_stat_scanned(lruvec, file, nr_taken); __count_vm_events(PGREFILL, nr_scanned); count_memcg_events(lruvec_memcg(lruvec), PGREFILL, nr_scanned); @@ -1989,7 +1986,7 @@ static void shrink_active_list(unsigned long nr_to_scan, * helps balance scan pressure between file and anonymous pages in * get_scan_count. */ - reclaim_stat->recent_rotated[file] += nr_rotated; + update_reclaim_stat_rotated(lruvec, file, nr_rotated); nr_activate = move_active_pages_to_lru(lruvec, &l_active, &l_hold, lru); nr_deactivate = move_active_pages_to_lru(lruvec, &l_inactive, &l_hold, lru - LRU_ACTIVE); @@ -2116,7 +2113,7 @@ static void get_scan_count(struct lruvec *lruvec, struct mem_cgroup *memcg, unsigned long *lru_pages) { int swappiness = mem_cgroup_swappiness(memcg); - struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat; + struct zone_reclaim_stat *rstat = &lruvec->reclaim_stat; u64 fraction[2]; u64 denominator = 0; /* gcc */ struct pglist_data *pgdat = lruvec_pgdat(lruvec); @@ -2125,6 +2122,7 @@ static void get_scan_count(struct lruvec *lruvec, struct mem_cgroup *memcg, unsigned long anon, file; unsigned long ap, fp; enum lru_list lru; + long recent_scanned[2], recent_rotated[2]; /* If we have no swap space, do not bother scanning anon pages. */ if (!sc->may_swap || mem_cgroup_get_nr_swap_pages(memcg) <= 0) { @@ -2238,14 +2236,22 @@ static void get_scan_count(struct lruvec *lruvec, struct mem_cgroup *memcg, lruvec_lru_size(lruvec, LRU_INACTIVE_FILE, MAX_NR_ZONES); spin_lock_irq(&pgdat->lru_lock); - if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) { - reclaim_stat->recent_scanned[0] /= 2; - reclaim_stat->recent_rotated[0] /= 2; + recent_scanned[0] = atomic_long_read(&rstat->recent_scanned[0]); + recent_rotated[0] = atomic_long_read(&rstat->recent_rotated[0]); + if (unlikely(recent_scanned[0] > anon / 4)) { + recent_scanned[0] /= 2; + recent_rotated[0] /= 2; + atomic_long_set(&rstat->recent_scanned[0], recent_scanned[0]); + atomic_long_set(&rstat->recent_rotated[0], recent_rotated[0]); } - if (unlikely(reclaim_stat->recent_scanned[1] > file / 4)) { - reclaim_stat->recent_scanned[1] /= 2; - reclaim_stat->recent_rotated[1] /= 2; + recent_scanned[1] = atomic_long_read(&rstat->recent_scanned[1]); + recent_rotated[1] = atomic_long_read(&rstat->recent_rotated[1]); + if (unlikely(recent_scanned[1] > file / 4)) { + recent_scanned[1] /= 2; + recent_rotated[1] /= 2; + atomic_long_set(&rstat->recent_scanned[1], recent_scanned[1]); + atomic_long_set(&rstat->recent_rotated[1], recent_rotated[1]); } /* @@ -2253,11 +2259,11 @@ static void get_scan_count(struct lruvec *lruvec, struct mem_cgroup *memcg, * proportional to the fraction of recently scanned pages on * each list that were recently referenced and in active use. */ - ap = anon_prio * (reclaim_stat->recent_scanned[0] + 1); - ap /= reclaim_stat->recent_rotated[0] + 1; + ap = anon_prio * (recent_scanned[0] + 1); + ap /= recent_rotated[0] + 1; - fp = file_prio * (reclaim_stat->recent_scanned[1] + 1); - fp /= reclaim_stat->recent_rotated[1] + 1; + fp = file_prio * (recent_scanned[1] + 1); + fp /= recent_rotated[1] + 1; spin_unlock_irq(&pgdat->lru_lock); fraction[0] = ap; -- 2.18.0
