[RFC 09/10] autonuma, memory tiering: Double hot threshold for write hint page fault

[Huang, Ying]

From: Huang Ying <ying.huang@xxxxxxxxx>

The write performance of PMEM is much worse than its read
performance.  So even if a write-mostly pages is colder than a
read-mostly pages, it is usually better to put the write-mostly pages
in DRAM and read-mostly pages in PMEM.

To give write-mostly pages more opportunity to be promoted to DRAM, in
this patch, the hot threshold for write hint page fault is
doubled (easier to be promoted).

Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Fengguang Wu <fengguang.wu@xxxxxxxxx>
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: linux-mm@xxxxxxxxx
---
 include/linux/sched/numa_balancing.h | 1 +
 kernel/sched/fair.c                  | 2 ++
 mm/memory.c                          | 3 +++
 3 files changed, 6 insertions(+)

diff --git a/include/linux/sched/numa_balancing.h b/include/linux/sched/numa_balancing.h
index e1c2728d5bb2..65dc8c6e8377 100644
--- a/include/linux/sched/numa_balancing.h
+++ b/include/linux/sched/numa_balancing.h
@@ -15,6 +15,7 @@
 #define TNF_FAULT_LOCAL	0x08
 #define TNF_MIGRATE_FAIL 0x10
 #define TNF_YOUNG	0x20
+#define TNF_WRITE	0x40
 
 #ifdef CONFIG_NUMA_BALANCING
 extern void task_numa_fault(int last_node, int node, int pages, int flags);
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index d6cf5832556e..0a83e9cf6685 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1513,6 +1513,8 @@ bool should_numa_migrate_memory(struct task_struct *p, struct page * page,
 
 		threshold = msecs_to_jiffies(
 			sysctl_numa_balancing_hot_threshold);
+		if (flags & TNF_WRITE)
+			threshold *= 2;
 		latency = numa_hint_fault_latency(p, addr);
 		if (latency > threshold)
 			return false;
diff --git a/mm/memory.c b/mm/memory.c
index 80902ff7f5de..fed6c943ba60 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3729,6 +3729,9 @@ static vm_fault_t do_numa_page(struct vm_fault *vmf)
 	if (pte_young(old_pte))
 		flags |= TNF_YOUNG;
 
+	if (vmf->flags & FAULT_FLAG_WRITE)
+		flags |= TNF_WRITE;
+
 	page = vm_normal_page(vma, vmf->address, pte);
 	if (!page)
 		goto unmap_out;
-- 
2.23.0