From efaffc5e40aeced0bcb497ed7a0a5b8c14abfcdf Mon Sep 17 00:00:00 2001
From: Mel Gorman <mgorman@techsingularity.net>
Date: Mon, 1 Oct 2018 11:05:24 +0100
Subject: [PATCH] mm, sched/numa: Remove rate-limiting of automatic NUMA
balancing migration
References: bnc#1101669 optimise numa balancing for fast migrate
Patch-mainline: v4.19-rc7
Git-commit: efaffc5e40aeced0bcb497ed7a0a5b8c14abfcdf
Rate limiting of page migrations due to automatic NUMA balancing was
introduced to mitigate the worst-case scenario of migrating at high
frequency due to false sharing or slowly ping-ponging between nodes.
Since then, a lot of effort was spent on correctly identifying these
pages and avoiding unnecessary migrations and the safety net may no longer
be required.
Jirka Hladky reported a regression in 4.17 due to a scheduler patch that
avoids spreading STREAM tasks wide prematurely. However, once the task
was properly placed, it delayed migrating the memory due to rate limiting.
Increasing the limit fixed the problem for him.
Currently, the limit is hard-coded and does not account for the real
capabilities of the hardware. Even if an estimate was attempted, it would
not properly account for the number of memory controllers and it could
not account for the amount of bandwidth used for normal accesses. Rather
than fudging, this patch simply eliminates the rate limiting.
However, Jirka reports that a STREAM configuration using multiple
processes achieved similar performance to 4.16. In local tests, this patch
improved performance of STREAM relative to the baseline but it is somewhat
machine-dependent. Most workloads show little or not performance difference
implying that there is not a heavily reliance on the throttling mechanism
and it is safe to remove.
STREAM on 2-socket machine
4.19.0-rc5 4.19.0-rc5
numab-v1r1 noratelimit-v1r1
MB/sec copy 43298.52 ( 0.00%) 44673.38 ( 3.18%)
MB/sec scale 30115.06 ( 0.00%) 31293.06 ( 3.91%)
MB/sec add 32825.12 ( 0.00%) 34883.62 ( 6.27%)
MB/sec triad 32549.52 ( 0.00%) 34906.60 ( 7.24%
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Reviewed-by: Rik van Riel <riel@surriel.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Jirka Hladky <jhladky@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Linux-MM <linux-mm@kvack.org>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20181001100525.29789-2-mgorman@techsingularity.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Mel Gorman <mgorman@suse.de>
---
include/linux/mmzone.h | 6 ----
include/trace/events/migrate.h | 27 ------------------
mm/migrate.c | 65 ------------------------------------------
mm/page_alloc.c | 2 --
4 files changed, 100 deletions(-)
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index ff1209154ee9..39d74cac0827 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -672,12 +672,6 @@ typedef struct pglist_data {
#ifdef CONFIG_NUMA_BALANCING
/* Lock serializing the migrate rate limiting window */
spinlock_t numabalancing_migrate_lock;
-
- /* Rate limiting time interval */
- unsigned long numabalancing_migrate_next_window;
-
- /* Number of pages migrated during the rate limiting time interval */
- unsigned long numabalancing_migrate_nr_pages;
#endif
/*
* This is a per-node reserve of pages that are not available
diff --git a/include/trace/events/migrate.h b/include/trace/events/migrate.h
index 539b25a76111..30fe0938d83f 100644
--- a/include/trace/events/migrate.h
+++ b/include/trace/events/migrate.h
@@ -69,33 +69,6 @@ TRACE_EVENT(mm_migrate_pages,
__print_symbolic(__entry->mode, MIGRATE_MODE),
__print_symbolic(__entry->reason, MIGRATE_REASON))
);
-
-TRACE_EVENT(mm_numa_migrate_ratelimit,
-
- TP_PROTO(struct task_struct *p, int dst_nid, unsigned long nr_pages),
-
- TP_ARGS(p, dst_nid, nr_pages),
-
- TP_STRUCT__entry(
- __array( char, comm, TASK_COMM_LEN)
- __field( pid_t, pid)
- __field( int, dst_nid)
- __field( unsigned long, nr_pages)
- ),
-
- TP_fast_assign(
- memcpy(__entry->comm, p->comm, TASK_COMM_LEN);
- __entry->pid = p->pid;
- __entry->dst_nid = dst_nid;
- __entry->nr_pages = nr_pages;
- ),
-
- TP_printk("comm=%s pid=%d dst_nid=%d nr_pages=%lu",
- __entry->comm,
- __entry->pid,
- __entry->dst_nid,
- __entry->nr_pages)
-);
#endif /* _TRACE_MIGRATE_H */
/* This part must be outside protection */
diff --git a/mm/migrate.c b/mm/migrate.c
index 5bcdaab5b220..ac1cdb8fa499 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1798,54 +1798,6 @@ static struct page *alloc_misplaced_dst_page(struct page *page,
return newpage;
}
-/*
- * page migration rate limiting control.
- * Do not migrate more than @pages_to_migrate in a @migrate_interval_millisecs
- * window of time. Default here says do not migrate more than 1280M per second.
- */
-static unsigned int migrate_interval_millisecs __read_mostly = 100;
-static unsigned int ratelimit_pages __read_mostly = 128 << (20 - PAGE_SHIFT);
-
-/* Returns true if the node is migrate rate-limited after the update */
-static bool numamigrate_update_ratelimit(pg_data_t *pgdat,
- unsigned long nr_pages)
-{
- unsigned long next_window, interval;
-
- next_window = READ_ONCE(pgdat->numabalancing_migrate_next_window);
- interval = msecs_to_jiffies(migrate_interval_millisecs);
-
- /*
- * Rate-limit the amount of data that is being migrated to a node.
- * Optimal placement is no good if the memory bus is saturated and
- * all the time is being spent migrating!
- */
- if (time_after(jiffies, next_window) &&
- spin_trylock(&pgdat->numabalancing_migrate_lock)) {
- pgdat->numabalancing_migrate_nr_pages = 0;
- do {
- next_window += interval;
- } while (unlikely(time_after(jiffies, next_window)));
-
- WRITE_ONCE(pgdat->numabalancing_migrate_next_window, next_window);
- spin_unlock(&pgdat->numabalancing_migrate_lock);
- }
- if (pgdat->numabalancing_migrate_nr_pages > ratelimit_pages) {
- trace_mm_numa_migrate_ratelimit(current, pgdat->node_id,
- nr_pages);
- return true;
- }
-
- /*
- * This is an unlocked non-atomic update so errors are possible.
- * The consequences are failing to migrate when we potentiall should
- * have which is not severe enough to warrant locking. If it is ever
- * a problem, it can be converted to a per-cpu counter.
- */
- pgdat->numabalancing_migrate_nr_pages += nr_pages;
- return false;
-}
-
static int numamigrate_isolate_page(pg_data_t *pgdat, struct page *page)
{
int page_lru;
@@ -1918,14 +1870,6 @@ int migrate_misplaced_page(struct page *page, struct vm_area_struct *vma,
if (page_is_file_cache(page) && PageDirty(page))
goto out;
- /*
- * Rate-limit the amount of data that is being migrated to a node.
- * Optimal placement is no good if the memory bus is saturated and
- * all the time is being spent migrating!
- */
- if (numamigrate_update_ratelimit(pgdat, 1))
- goto out;
-
isolated = numamigrate_isolate_page(pgdat, page);
if (!isolated)
goto out;
@@ -1973,14 +1917,6 @@ int migrate_misplaced_transhuge_page(struct mm_struct *mm,
unsigned long mmun_end = mmun_start + HPAGE_PMD_SIZE;
pmd_t orig_entry;
- /*
- * Rate-limit the amount of data that is being migrated to a node.
- * Optimal placement is no good if the memory bus is saturated and
- * all the time is being spent migrating!
- */
- if (numamigrate_update_ratelimit(pgdat, HPAGE_PMD_NR))
- goto out_dropref;
-
new_page = alloc_pages_node(node,
(GFP_TRANSHUGE_LIGHT | __GFP_THISNODE),
HPAGE_PMD_ORDER);
@@ -2083,7 +2019,6 @@ int migrate_misplaced_transhuge_page(struct mm_struct *mm,
out_fail:
count_vm_events(PGMIGRATE_FAIL, HPAGE_PMD_NR);
-out_dropref:
ptl = pmd_lock(mm, pmd);
if (pmd_same(*pmd, entry)) {
entry = pmd_modify(entry, vma->vm_page_prot);
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index f1e3530da6b7..9cdeb2b80e9a 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6102,8 +6102,6 @@ static void __paginginit free_area_init_core(struct pglist_data *pgdat)
pgdat_resize_init(pgdat);
#ifdef CONFIG_NUMA_BALANCING
spin_lock_init(&pgdat->numabalancing_migrate_lock);
- pgdat->numabalancing_migrate_nr_pages = 0;
- pgdat->numabalancing_migrate_next_window = jiffies;
#endif
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
spin_lock_init(&pgdat->split_queue_lock);
--
2.13.7