[RFC PATCH 03/25] mm: migrate: Add a multi-threaded page migration function.

[Zi Yan]

From: Zi Yan <ziy@xxxxxxxxxx>

copy_page_multithread() function is added to migrate huge pages
in multi-threaded way, which provides higher throughput than
a single-threaded way.

Internally, copy_page_multithread() splits and distributes a huge page
into multiple threads, then send them as jobs to system_highpri_wq.

Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
---
 include/linux/highmem.h |   2 +
 mm/Makefile             |   2 +
 mm/copy_page.c          | 128 ++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 132 insertions(+)
 create mode 100644 mm/copy_page.c

diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index ea5cdbd8c..0f50dc5 100644
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -276,4 +276,6 @@ static inline void copy_highpage(struct page *to, struct page *from)
 
 #endif
 
+int copy_page_multithread(struct page *to, struct page *from, int nr_pages);
+
 #endif /* _LINUX_HIGHMEM_H */
diff --git a/mm/Makefile b/mm/Makefile
index d210cc9..fa02a9f 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -44,6 +44,8 @@ obj-y			:= filemap.o mempool.o oom_kill.o fadvise.o \
 obj-y += init-mm.o
 obj-y += memblock.o
 
+obj-y += copy_page.o
+
 ifdef CONFIG_MMU
 	obj-$(CONFIG_ADVISE_SYSCALLS)	+= madvise.o
 endif
diff --git a/mm/copy_page.c b/mm/copy_page.c
new file mode 100644
index 0000000..9cf849c
--- /dev/null
+++ b/mm/copy_page.c
@@ -0,0 +1,128 @@
+/*
+ * Enhanced page copy routine.
+ *
+ * Copyright 2019 by NVIDIA.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * Authors: Zi Yan <ziy@xxxxxxxxxx>
+ *
+ */
+
+#include <linux/highmem.h>
+#include <linux/workqueue.h>
+#include <linux/slab.h>
+#include <linux/freezer.h>
+
+
+const unsigned int limit_mt_num = 4;
+
+/* ======================== multi-threaded copy page ======================== */
+
+struct copy_item {
+	char *to;
+	char *from;
+	unsigned long chunk_size;
+};
+
+struct copy_page_info {
+	struct work_struct copy_page_work;
+	unsigned long num_items;
+	struct copy_item item_list[0];
+};
+
+static void copy_page_routine(char *vto, char *vfrom,
+	unsigned long chunk_size)
+{
+	memcpy(vto, vfrom, chunk_size);
+}
+
+static void copy_page_work_queue_thread(struct work_struct *work)
+{
+	struct copy_page_info *my_work = (struct copy_page_info *)work;
+	int i;
+
+	for (i = 0; i < my_work->num_items; ++i)
+		copy_page_routine(my_work->item_list[i].to,
+						  my_work->item_list[i].from,
+						  my_work->item_list[i].chunk_size);
+}
+
+int copy_page_multithread(struct page *to, struct page *from, int nr_pages)
+{
+	unsigned int total_mt_num = limit_mt_num;
+	int to_node = page_to_nid(to);
+	int i;
+	struct copy_page_info *work_items[NR_CPUS] = {0};
+	char *vto, *vfrom;
+	unsigned long chunk_size;
+	const struct cpumask *per_node_cpumask = cpumask_of_node(to_node);
+	int cpu_id_list[NR_CPUS] = {0};
+	int cpu;
+	int err = 0;
+
+	total_mt_num = min_t(unsigned int, total_mt_num,
+						 cpumask_weight(per_node_cpumask));
+	if (total_mt_num > 1)
+		total_mt_num = (total_mt_num / 2) * 2;
+
+	if (total_mt_num > num_online_cpus() || total_mt_num <=1)
+		return -ENODEV;
+
+	for (cpu = 0; cpu < total_mt_num; ++cpu) {
+		work_items[cpu] = kzalloc(sizeof(struct copy_page_info)
+						+ sizeof(struct copy_item), GFP_KERNEL);
+		if (!work_items[cpu]) {
+			err = -ENOMEM;
+			goto free_work_items;
+		}
+	}
+
+	i = 0;
+	for_each_cpu(cpu, per_node_cpumask) {
+		if (i >= total_mt_num)
+			break;
+		cpu_id_list[i] = cpu;
+		++i;
+	}
+
+	vfrom = kmap(from);
+	vto = kmap(to);
+	chunk_size = PAGE_SIZE*nr_pages / total_mt_num;
+
+	for (i = 0; i < total_mt_num; ++i) {
+		INIT_WORK((struct work_struct *)work_items[i],
+				  copy_page_work_queue_thread);
+
+		work_items[i]->num_items = 1;
+		work_items[i]->item_list[0].to = vto + i * chunk_size;
+		work_items[i]->item_list[0].from = vfrom + i * chunk_size;
+		work_items[i]->item_list[0].chunk_size = chunk_size;
+
+		queue_work_on(cpu_id_list[i],
+					  system_highpri_wq,
+					  (struct work_struct *)work_items[i]);
+	}
+
+	/* Wait until it finishes  */
+	for (i = 0; i < total_mt_num; ++i)
+		flush_work((struct work_struct *)work_items[i]);
+
+	kunmap(to);
+	kunmap(from);
+
+free_work_items:
+	for (cpu = 0; cpu < total_mt_num; ++cpu)
+		if (work_items[cpu])
+			kfree(work_items[cpu]);
+
+	return err;
+}
-- 
2.7.4