@@ -623,6 +623,17 @@ different types of memory (represented as different NUMA nodes) to
place the hot pages in the fast memory. This is implemented based on
unmapping and page fault too.
+numa_balancing_promote_rate_limit_MBps
+======================================
+
+Too high promotion/demotion throughput between different memory types
+may hurt application latency. This can be used to rate limit the
+promotion throughput. The per-node max promotion throughput in MB/s
+will be limited to be no more than the set value.
+
+A rule of thumb is to set this to less than 1/10 of the PMEM node
+write bandwidth.
+
oops_all_cpu_backtrace
======================
@@ -224,6 +224,7 @@ enum node_stat_item {
#endif
#ifdef CONFIG_NUMA_BALANCING
PGPROMOTE_SUCCESS, /* promote successfully */
+ PGPROMOTE_CANDIDATE, /* candidate pages to promote */
#endif
NR_VM_NODE_STAT_ITEMS
};
@@ -915,6 +916,11 @@ typedef struct pglist_data {
struct deferred_split deferred_split_queue;
#endif
+#ifdef CONFIG_NUMA_BALANCING
+ unsigned long numa_nr_candidate; /* number of promote candidate pages at
+ * rate limit start time */
+ unsigned int numa_ts; /* promote rate limit start time in ms */
+#endif
/* Fields commonly accessed by the page reclaim scanner */
/*
@@ -29,6 +29,7 @@ enum sched_tunable_scaling {
#ifdef CONFIG_NUMA_BALANCING
extern int sysctl_numa_balancing_mode;
+extern unsigned int sysctl_numa_balancing_promote_rate_limit;
#else
#define sysctl_numa_balancing_mode 0
#endif
@@ -1061,6 +1061,9 @@ 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;
@@ -1465,6 +1468,29 @@ 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_candidate;
+ unsigned int now, last_ts;
+
+ now = jiffies_to_msecs(jiffies);
+ mod_node_page_state(pgdat, PGPROMOTE_CANDIDATE, nr);
+ nr_candidate = node_page_state(pgdat, PGPROMOTE_CANDIDATE);
+ last_ts = pgdat->numa_ts;
+ if (now - last_ts > MSEC_PER_SEC &&
+ cmpxchg(&pgdat->numa_ts, last_ts, now) == last_ts)
+ pgdat->numa_nr_candidate = nr_candidate;
+ if (nr_candidate - pgdat->numa_nr_candidate >= rate_limit)
+ return true;
+ return false;
+}
+
bool should_numa_migrate_memory(struct task_struct *p, struct page * page,
int src_nid, int dst_cpu)
{
@@ -1479,7 +1505,7 @@ 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))
@@ -1490,7 +1516,10 @@ 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);
@@ -1698,6 +1698,14 @@ static struct ctl_table kern_table[] = {
.extra1 = SYSCTL_ZERO,
.extra2 = SYSCTL_FOUR,
},
+ {
+ .procname = "numa_balancing_promote_rate_limit_MBps",
+ .data = &sysctl_numa_balancing_promote_rate_limit,
+ .maxlen = sizeof(unsigned int),
+ .mode = 0644,
+ .proc_handler = proc_dointvec_minmax,
+ .extra1 = SYSCTL_ZERO,
+ },
#endif /* CONFIG_NUMA_BALANCING */
{
.procname = "sched_rt_period_us",
@@ -1245,6 +1245,7 @@ const char * const vmstat_text[] = {
#endif
#ifdef CONFIG_NUMA_BALANCING
"pgpromote_success",
+ "pgpromote_candidate",
#endif
/* enum writeback_stat_item counters */
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. Signed-off-by: "Huang, Ying" <ying.huang@intel.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Michal Hocko <mhocko@suse.com> Cc: Rik van Riel <riel@surriel.com> Cc: Mel Gorman <mgorman@techsingularity.net> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Yang Shi <shy828301@gmail.com> Cc: Zi Yan <ziy@nvidia.com> Cc: Wei Xu <weixugc@google.com> Cc: osalvador <osalvador@suse.de> Cc: Shakeel Butt <shakeelb@google.com> Cc: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org --- Documentation/admin-guide/sysctl/kernel.rst | 11 +++++++ include/linux/mmzone.h | 6 ++++ include/linux/sched/sysctl.h | 1 + kernel/sched/fair.c | 33 +++++++++++++++++++-- kernel/sysctl.c | 8 +++++ mm/vmstat.c | 1 + 6 files changed, 58 insertions(+), 2 deletions(-)