memory tiering: rate limit NUMA migration throughput

In NUMA balancing memory tiering mode, if there are hot pages in slow
memory node and cold pages in fast memory node, we need to promote/demote
hot/cold pages between the fast and cold memory nodes.

A choice is to promote/demote as fast as possible.  But the CPU cycles and
memory bandwidth consumed by the high promoting/demoting throughput will
hurt the latency of some workload because of accessing inflating and slow
memory bandwidth contention.

A way to resolve this issue is to restrict the max promoting/demoting
throughput.  It will take longer to finish the promoting/demoting.  But
the workload latency will be better.  This is implemented in this patch as
the page promotion rate limit mechanism.

The number of the candidate pages to be promoted to the fast memory node
via NUMA balancing is counted, if the count exceeds the limit specified by
the users, the NUMA balancing promotion will be stopped until the next
second.

A new sysctl knob kernel.numa_balancing_promote_rate_limit_MBps is added
for the users to specify the limit.

Link: https://lkml.kernel.org/r/20220713083954.34196-3-ying.huang@intel.com
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Tested-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Michal Hocko <mhocko@suse.com>
Cc: osalvador <osalvador@suse.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Wei Xu <weixugc@google.com>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Zhong Jiang <zhongjiang-ali@linux.alibaba.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 31 insertions, 2 deletions

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 06db566c7660..1d1dd88daaab 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1097,6 +1097,9 @@ unsigned int sysctl_numa_balancing_scan_delay = 1000;
 /* The page with hint page fault latency < threshold in ms is considered hot */
 unsigned int sysctl_numa_balancing_hot_threshold = MSEC_PER_SEC;
 
+/* Restrict the NUMA promotion throughput (MB/s) for each target node. */
+unsigned int sysctl_numa_balancing_promote_rate_limit = 65536;
+
 struct numa_group {
 	refcount_t refcount;
 
@@ -1501,6 +1504,29 @@ static int numa_hint_fault_latency(struct page *page)
 	return (time - last_time) & PAGE_ACCESS_TIME_MASK;
 }
 
+/*
+ * For memory tiering mode, too high promotion/demotion throughput may
+ * hurt application latency.  So we provide a mechanism to rate limit
+ * the number of pages that are tried to be promoted.
+ */
+static bool numa_promotion_rate_limit(struct pglist_data *pgdat,
+				      unsigned long rate_limit, int nr)
+{
+	unsigned long nr_cand;
+	unsigned int now, start;
+
+	now = jiffies_to_msecs(jiffies);
+	mod_node_page_state(pgdat, PGPROMOTE_CANDIDATE, nr);
+	nr_cand = node_page_state(pgdat, PGPROMOTE_CANDIDATE);
+	start = pgdat->nbp_rl_start;
+	if (now - start > MSEC_PER_SEC &&
+	    cmpxchg(&pgdat->nbp_rl_start, start, now) == start)
+		pgdat->nbp_rl_nr_cand = nr_cand;
+	if (nr_cand - pgdat->nbp_rl_nr_cand >= rate_limit)
+		return true;
+	return false;
+}
+
 bool should_numa_migrate_memory(struct task_struct *p, struct page * page,
 				int src_nid, int dst_cpu)
 {
@@ -1515,7 +1541,7 @@ bool should_numa_migrate_memory(struct task_struct *p, struct page * page,
 	if (sysctl_numa_balancing_mode & NUMA_BALANCING_MEMORY_TIERING &&
 	    !node_is_toptier(src_nid)) {
 		struct pglist_data *pgdat;
-		unsigned long latency, th;
+		unsigned long rate_limit, latency, th;
 
 		pgdat = NODE_DATA(dst_nid);
 		if (pgdat_free_space_enough(pgdat))
@@ -1526,7 +1552,10 @@ bool should_numa_migrate_memory(struct task_struct *p, struct page * page,
 		if (latency >= th)
 			return false;
 
-		return true;
+		rate_limit = sysctl_numa_balancing_promote_rate_limit << \
+			(20 - PAGE_SHIFT);
+		return !numa_promotion_rate_limit(pgdat, rate_limit,
+						  thp_nr_pages(page));
 	}
 
 	this_cpupid = cpu_pid_to_cpupid(dst_cpu, current->pid);