[PATCH v3] mm/khugepaged: sched to numa node when collapse huge page

[Bibo Mao <maobibo@loongson.cn>]

collapse huge page will copy huge page from general small pages,
dest node is calculated from most one of source pages, however
THP daemon is not scheduled on dest node. The performance may be
poor since huge page copying across nodes, also cache is not used
for target node. With this patch, khugepaged daemon switches to
the same numa node with huge page. It saves copying time and makes
use of local cache better.

With this patch, specint 2006 base performance is improved with 6%
on Loongson 3C5000L platform with 32 cores and 8 numa nodes.

Signed-off-by: Bibo Mao <maobibo@loongson.cn>
---
changelog:
V2: remove node record for thp daemon
V3: remove unlikely statement
---
 mm/khugepaged.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 131492fd1148..b3cf0885f5a2 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1066,6 +1066,7 @@ static void collapse_huge_page(struct mm_struct *mm,
 	struct vm_area_struct *vma;
 	struct mmu_notifier_range range;
 	gfp_t gfp;
+	const struct cpumask *cpumask;
 
 	VM_BUG_ON(address & ~HPAGE_PMD_MASK);
 
@@ -1079,6 +1080,13 @@ static void collapse_huge_page(struct mm_struct *mm,
 	 * that. We will recheck the vma after taking it again in write mode.
 	 */
 	mmap_read_unlock(mm);
+
+	/* sched to specified node before huage page memory copy */
+	if (task_node(current) != node) {
+		cpumask = cpumask_of_node(node);
+		if (!cpumask_empty(cpumask))
+			set_cpus_allowed_ptr(current, cpumask);
+	}
 	new_page = khugepaged_alloc_page(hpage, gfp, node);
 	if (!new_page) {
 		result = SCAN_ALLOC_HUGE_PAGE_FAIL;
-- 
2.31.1