From 698b1b30642f1ff0ea10ef1de9745ab633031377 Mon Sep 17 00:00:00 2001 From: Vlastimil Babka Date: Thu, 17 Mar 2016 14:18:08 -0700 Subject: [PATCH] mm, compaction: introduce kcompactd Memory compaction can be currently performed in several contexts: - kswapd balancing a zone after a high-order allocation failure - direct compaction to satisfy a high-order allocation, including THP page fault attemps - khugepaged trying to collapse a hugepage - manually from /proc The purpose of compaction is two-fold. The obvious purpose is to satisfy a (pending or future) high-order allocation, and is easy to evaluate. The other purpose is to keep overal memory fragmentation low and help the anti-fragmentation mechanism. The success wrt the latter purpose is more The current situation wrt the purposes has a few drawbacks: - compaction is invoked only when a high-order page or hugepage is not available (or manually). This might be too late for the purposes of keeping memory fragmentation low. - direct compaction increases latency of allocations. Again, it would be better if compaction was performed asynchronously to keep fragmentation low, before the allocation itself comes. - (a special case of the previous) the cost of compaction during THP page faults can easily offset the benefits of THP. - kswapd compaction appears to be complex, fragile and not working in some scenarios. It could also end up compacting for a high-order allocation request when it should be reclaiming memory for a later order-0 request. To improve the situation, we should be able to benefit from an equivalent of kswapd, but for compaction - i.e. a background thread which responds to fragmentation and the need for high-order allocations (including hugepages) somewhat proactively. One possibility is to extend the responsibilities of kswapd, which could however complicate its design too much. It should be better to let kswapd handle reclaim, as order-0 allocations are often more critical than high-order ones. Another possibility is to extend khugepaged, but this kthread is a single instance and tied to THP configs. This patch goes with the option of a new set of per-node kthreads called kcompactd, and lays the foundations, without introducing any new tunables. The lifecycle mimics kswapd kthreads, including the memory hotplug hooks. For compaction, kcompactd uses the standard compaction_suitable() and ompact_finished() criteria and the deferred compaction functionality. Unlike direct compaction, it uses only sync compaction, as there's no allocation latency to minimize. This patch doesn't yet add a call to wakeup_kcompactd. The kswapd compact/reclaim loop for high-order pages will be replaced by waking up kcompactd in the next patch with the description of what's wrong with the old approach. Waking up of the kcompactd threads is also tied to kswapd activity and follows these rules: - we don't want to affect any fastpaths, so wake up kcompactd only from the slowpath, as it's done for kswapd - if kswapd is doing reclaim, it's more important than compaction, so don't invoke kcompactd until kswapd goes to sleep - the target order used for kswapd is passed to kcompactd Future possible future uses for kcompactd include the ability to wake up kcompactd on demand in special situations, such as when hugepages are not available (currently not done due to __GFP_NO_KSWAPD) or when a fragmentation event (i.e. __rmqueue_fallback()) occurs. It's also possible to perform periodic compaction with kcompactd. [arnd@arndb.de: fix build errors with kcompactd] [paul.gortmaker@windriver.com: don't use modular references for non modular code] Signed-off-by: Vlastimil Babka Cc: Andrea Arcangeli Cc: "Kirill A. Shutemov" Cc: Rik van Riel Cc: Joonsoo Kim Cc: Mel Gorman Cc: David Rientjes Cc: Michal Hocko Cc: Johannes Weiner Signed-off-by: Arnd Bergmann Signed-off-by: Paul Gortmaker Cc: Hugh Dickins Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/compaction.h | 16 +++ include/linux/mmzone.h | 6 + include/linux/vm_event_item.h | 1 + include/trace/events/compaction.h | 55 ++++++++ mm/compaction.c | 222 ++++++++++++++++++++++++++++++ mm/memory_hotplug.c | 9 +- mm/page_alloc.c | 3 + mm/vmstat.c | 1 + 8 files changed, 311 insertions(+), 2 deletions(-) diff --git a/include/linux/compaction.h b/include/linux/compaction.h index 4cd4ddf64cc7..d7c8de583a23 100644 --- a/include/linux/compaction.h +++ b/include/linux/compaction.h @@ -52,6 +52,10 @@ extern void compaction_defer_reset(struct zone *zone, int order, bool alloc_success); extern bool compaction_restarting(struct zone *zone, int order); +extern int kcompactd_run(int nid); +extern void kcompactd_stop(int nid); +extern void wakeup_kcompactd(pg_data_t *pgdat, int order, int classzone_idx); + #else static inline unsigned long try_to_compact_pages(gfp_t gfp_mask, unsigned int order, int alloc_flags, @@ -84,6 +88,18 @@ static inline bool compaction_deferred(struct zone *zone, int order) return true; } +static inline int kcompactd_run(int nid) +{ + return 0; +} +static inline void kcompactd_stop(int nid) +{ +} + +static inline void wakeup_kcompactd(pg_data_t *pgdat, int order, int classzone_idx) +{ +} + #endif /* CONFIG_COMPACTION */ #if defined(CONFIG_COMPACTION) && defined(CONFIG_SYSFS) && defined(CONFIG_NUMA) diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index 6de02ac378a0..bdd9a270a813 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -668,6 +668,12 @@ typedef struct pglist_data { mem_hotplug_begin/end() */ int kswapd_max_order; enum zone_type classzone_idx; +#ifdef CONFIG_COMPACTION + int kcompactd_max_order; + enum zone_type kcompactd_classzone_idx; + wait_queue_head_t kcompactd_wait; + struct task_struct *kcompactd; +#endif #ifdef CONFIG_NUMA_BALANCING /* Lock serializing the migrate rate limiting window */ spinlock_t numabalancing_migrate_lock; diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h index 67c1dbd19c6d..58ecc056ee45 100644 --- a/include/linux/vm_event_item.h +++ b/include/linux/vm_event_item.h @@ -53,6 +53,7 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT, COMPACTMIGRATE_SCANNED, COMPACTFREE_SCANNED, COMPACTISOLATED, COMPACTSTALL, COMPACTFAIL, COMPACTSUCCESS, + KCOMPACTD_WAKE, #endif #ifdef CONFIG_HUGETLB_PAGE HTLB_BUDDY_PGALLOC, HTLB_BUDDY_PGALLOC_FAIL, diff --git a/include/trace/events/compaction.h b/include/trace/events/compaction.h index 111e5666e5eb..e215bf68f521 100644 --- a/include/trace/events/compaction.h +++ b/include/trace/events/compaction.h @@ -350,6 +350,61 @@ DEFINE_EVENT(mm_compaction_defer_template, mm_compaction_defer_reset, ); #endif +TRACE_EVENT(mm_compaction_kcompactd_sleep, + + TP_PROTO(int nid), + + TP_ARGS(nid), + + TP_STRUCT__entry( + __field(int, nid) + ), + + TP_fast_assign( + __entry->nid = nid; + ), + + TP_printk("nid=%d", __entry->nid) +); + +DECLARE_EVENT_CLASS(kcompactd_wake_template, + + TP_PROTO(int nid, int order, enum zone_type classzone_idx), + + TP_ARGS(nid, order, classzone_idx), + + TP_STRUCT__entry( + __field(int, nid) + __field(int, order) + __field(enum zone_type, classzone_idx) + ), + + TP_fast_assign( + __entry->nid = nid; + __entry->order = order; + __entry->classzone_idx = classzone_idx; + ), + + TP_printk("nid=%d order=%d classzone_idx=%-8s", + __entry->nid, + __entry->order, + __print_symbolic(__entry->classzone_idx, ZONE_TYPE)) +); + +DEFINE_EVENT(kcompactd_wake_template, mm_compaction_wakeup_kcompactd, + + TP_PROTO(int nid, int order, enum zone_type classzone_idx), + + TP_ARGS(nid, order, classzone_idx) +); + +DEFINE_EVENT(kcompactd_wake_template, mm_compaction_kcompactd_wake, + + TP_PROTO(int nid, int order, enum zone_type classzone_idx), + + TP_ARGS(nid, order, classzone_idx) +); + #endif /* _TRACE_COMPACTION_H */ /* This part must be outside protection */ diff --git a/mm/compaction.c b/mm/compaction.c index 93f71d968098..5b2bfbaa821a 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -7,6 +7,7 @@ * * Copyright IBM Corp. 2007-2010 Mel Gorman */ +#include #include #include #include @@ -17,6 +18,8 @@ #include #include #include +#include +#include #include "internal.h" #ifdef CONFIG_COMPACTION @@ -1736,4 +1739,223 @@ void compaction_unregister_node(struct node *node) } #endif /* CONFIG_SYSFS && CONFIG_NUMA */ +static inline bool kcompactd_work_requested(pg_data_t *pgdat) +{ + return pgdat->kcompactd_max_order > 0; +} + +static bool kcompactd_node_suitable(pg_data_t *pgdat) +{ + int zoneid; + struct zone *zone; + enum zone_type classzone_idx = pgdat->kcompactd_classzone_idx; + + for (zoneid = 0; zoneid < classzone_idx; zoneid++) { + zone = &pgdat->node_zones[zoneid]; + + if (!populated_zone(zone)) + continue; + + if (compaction_suitable(zone, pgdat->kcompactd_max_order, 0, + classzone_idx) == COMPACT_CONTINUE) + return true; + } + + return false; +} + +static void kcompactd_do_work(pg_data_t *pgdat) +{ + /* + * With no special task, compact all zones so that a page of requested + * order is allocatable. + */ + int zoneid; + struct zone *zone; + struct compact_control cc = { + .order = pgdat->kcompactd_max_order, + .classzone_idx = pgdat->kcompactd_classzone_idx, + .mode = MIGRATE_SYNC_LIGHT, + .ignore_skip_hint = true, + + }; + bool success = false; + + trace_mm_compaction_kcompactd_wake(pgdat->node_id, cc.order, + cc.classzone_idx); + count_vm_event(KCOMPACTD_WAKE); + + for (zoneid = 0; zoneid < cc.classzone_idx; zoneid++) { + int status; + + zone = &pgdat->node_zones[zoneid]; + if (!populated_zone(zone)) + continue; + + if (compaction_deferred(zone, cc.order)) + continue; + + if (compaction_suitable(zone, cc.order, 0, zoneid) != + COMPACT_CONTINUE) + continue; + + cc.nr_freepages = 0; + cc.nr_migratepages = 0; + cc.zone = zone; + INIT_LIST_HEAD(&cc.freepages); + INIT_LIST_HEAD(&cc.migratepages); + + status = compact_zone(zone, &cc); + + if (zone_watermark_ok(zone, cc.order, low_wmark_pages(zone), + cc.classzone_idx, 0)) { + success = true; + compaction_defer_reset(zone, cc.order, false); + } else if (status == COMPACT_COMPLETE) { + /* + * We use sync migration mode here, so we defer like + * sync direct compaction does. + */ + defer_compaction(zone, cc.order); + } + + VM_BUG_ON(!list_empty(&cc.freepages)); + VM_BUG_ON(!list_empty(&cc.migratepages)); + } + + /* + * Regardless of success, we are done until woken up next. But remember + * the requested order/classzone_idx in case it was higher/tighter than + * our current ones + */ + if (pgdat->kcompactd_max_order <= cc.order) + pgdat->kcompactd_max_order = 0; + if (pgdat->kcompactd_classzone_idx >= cc.classzone_idx) + pgdat->kcompactd_classzone_idx = pgdat->nr_zones - 1; +} + +void wakeup_kcompactd(pg_data_t *pgdat, int order, int classzone_idx) +{ + if (!order) + return; + + if (pgdat->kcompactd_max_order < order) + pgdat->kcompactd_max_order = order; + + if (pgdat->kcompactd_classzone_idx > classzone_idx) + pgdat->kcompactd_classzone_idx = classzone_idx; + + if (!waitqueue_active(&pgdat->kcompactd_wait)) + return; + + if (!kcompactd_node_suitable(pgdat)) + return; + + trace_mm_compaction_wakeup_kcompactd(pgdat->node_id, order, + classzone_idx); + wake_up_interruptible(&pgdat->kcompactd_wait); +} + +/* + * The background compaction daemon, started as a kernel thread + * from the init process. + */ +static int kcompactd(void *p) +{ + pg_data_t *pgdat = (pg_data_t*)p; + struct task_struct *tsk = current; + + const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id); + + if (!cpumask_empty(cpumask)) + set_cpus_allowed_ptr(tsk, cpumask); + + set_freezable(); + + pgdat->kcompactd_max_order = 0; + pgdat->kcompactd_classzone_idx = pgdat->nr_zones - 1; + + while (!kthread_should_stop()) { + trace_mm_compaction_kcompactd_sleep(pgdat->node_id); + wait_event_freezable(pgdat->kcompactd_wait, + kcompactd_work_requested(pgdat)); + + kcompactd_do_work(pgdat); + } + + return 0; +} + +/* + * This kcompactd start function will be called by init and node-hot-add. + * On node-hot-add, kcompactd will moved to proper cpus if cpus are hot-added. + */ +int kcompactd_run(int nid) +{ + pg_data_t *pgdat = NODE_DATA(nid); + int ret = 0; + + if (pgdat->kcompactd) + return 0; + + pgdat->kcompactd = kthread_run(kcompactd, pgdat, "kcompactd%d", nid); + if (IS_ERR(pgdat->kcompactd)) { + pr_err("Failed to start kcompactd on node %d\n", nid); + ret = PTR_ERR(pgdat->kcompactd); + pgdat->kcompactd = NULL; + } + return ret; +} + +/* + * Called by memory hotplug when all memory in a node is offlined. Caller must + * hold mem_hotplug_begin/end(). + */ +void kcompactd_stop(int nid) +{ + struct task_struct *kcompactd = NODE_DATA(nid)->kcompactd; + + if (kcompactd) { + kthread_stop(kcompactd); + NODE_DATA(nid)->kcompactd = NULL; + } +} + +/* + * It's optimal to keep kcompactd on the same CPUs as their memory, but + * not required for correctness. So if the last cpu in a node goes + * away, we get changed to run anywhere: as the first one comes back, + * restore their cpu bindings. + */ +static int cpu_callback(struct notifier_block *nfb, unsigned long action, + void *hcpu) +{ + int nid; + + if (action == CPU_ONLINE || action == CPU_ONLINE_FROZEN) { + for_each_node_state(nid, N_MEMORY) { + pg_data_t *pgdat = NODE_DATA(nid); + const struct cpumask *mask; + + mask = cpumask_of_node(pgdat->node_id); + + if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids) + /* One of our CPUs online: restore mask */ + set_cpus_allowed_ptr(pgdat->kcompactd, mask); + } + } + return NOTIFY_OK; +} + +static int __init kcompactd_init(void) +{ + int nid; + + for_each_node_state(nid, N_MEMORY) + kcompactd_run(nid); + hotcpu_notifier(cpu_callback, 0); + return 0; +} +subsys_initcall(kcompactd_init) + #endif /* CONFIG_COMPACTION */ diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c index 24ea06393816..d9bcb26fc4df 100644 --- a/mm/memory_hotplug.c +++ b/mm/memory_hotplug.c @@ -33,6 +33,7 @@ #include #include #include +#include #include @@ -1105,8 +1106,10 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages, int online_typ init_per_zone_wmark_min(); - if (onlined_pages) + if (onlined_pages) { kswapd_run(zone_to_nid(zone)); + kcompactd_run(nid); + } vm_total_pages = nr_free_pagecache_pages(); @@ -1880,8 +1883,10 @@ repeat: zone_pcp_update(zone); node_states_clear_node(node, &arg); - if (arg.status_change_nid >= 0) + if (arg.status_change_nid >= 0) { kswapd_stop(node); + kcompactd_stop(node); + } vm_total_pages = nr_free_pagecache_pages(); writeback_set_ratelimit(); diff --git a/mm/page_alloc.c b/mm/page_alloc.c index b1fc19ebb8a2..25a75da53c27 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -5405,6 +5405,9 @@ static void __paginginit free_area_init_core(struct pglist_data *pgdat) #endif init_waitqueue_head(&pgdat->kswapd_wait); init_waitqueue_head(&pgdat->pfmemalloc_wait); +#ifdef CONFIG_COMPACTION + init_waitqueue_head(&pgdat->kcompactd_wait); +#endif pgdat_page_ext_init(pgdat); for (j = 0; j < MAX_NR_ZONES; j++) { diff --git a/mm/vmstat.c b/mm/vmstat.c index 69ce64f7b8d7..f80066248c94 100644 --- a/mm/vmstat.c +++ b/mm/vmstat.c @@ -826,6 +826,7 @@ const char * const vmstat_text[] = { "compact_stall", "compact_fail", "compact_success", + "compact_daemon_wake", #endif #ifdef CONFIG_HUGETLB_PAGE -- 2.30.2