[RFC PATCH 13/25] exchange pages: add multi-threaded exchange pages.

[Zi Yan <zi.yan@sent.com>]

From: Zi Yan <ziy@nvidia.com>

Exchange two pages using multi threads. Exchange two lists of pages
using multi threads.

Signed-off-by: Zi Yan <ziy@nvidia.com>
---
 mm/Makefile        |   1 +
 mm/exchange.c      |  15 ++--
 mm/exchange_page.c | 229 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 mm/internal.h      |   5 ++
 4 files changed, 245 insertions(+), 5 deletions(-)
 create mode 100644 mm/exchange_page.c

diff --git a/mm/Makefile b/mm/Makefile
index 5e6c591..2f1f1ad 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -46,6 +46,7 @@ obj-y += memblock.o
 
 obj-y += copy_page.o
 obj-y += exchange.o
+obj-y += exchange_page.o
 
 ifdef CONFIG_MMU
 	obj-$(CONFIG_ADVISE_SYSCALLS)	+= madvise.o
diff --git a/mm/exchange.c b/mm/exchange.c
index 626bbea..ce2c899 100644
--- a/mm/exchange.c
+++ b/mm/exchange.c
@@ -345,11 +345,16 @@ static int exchange_from_to_pages(struct page *to_page, struct page *from_page,
 
 	rc = -EFAULT;
 
-	if (PageHuge(from_page) || PageTransHuge(from_page))
-		exchange_huge_page(to_page, from_page);
-	else
-		exchange_highpage(to_page, from_page);
-	rc = 0;
+	if (mode & MIGRATE_MT)
+		rc = exchange_page_mthread(to_page, from_page,
+				hpage_nr_pages(from_page));
+	if (rc) {
+		if (PageHuge(from_page) || PageTransHuge(from_page))
+			exchange_huge_page(to_page, from_page);
+		else
+			exchange_highpage(to_page, from_page);
+		rc = 0;
+	}
 
 	exchange_page_flags(to_page, from_page);
 
diff --git a/mm/exchange_page.c b/mm/exchange_page.c
new file mode 100644
index 0000000..6054697
--- /dev/null
+++ b/mm/exchange_page.c
@@ -0,0 +1,229 @@
+/*
+ * Exchange 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@nvidia.com>
+ *
+ */
+#include <linux/highmem.h>
+#include <linux/workqueue.h>
+#include <linux/slab.h>
+#include <linux/freezer.h>
+
+/*
+ * nr_copythreads can be the highest number of threads for given node
+ * on any architecture. The actual number of copy threads will be
+ * limited by the cpumask weight of the target node.
+ */
+extern unsigned int limit_mt_num;
+
+struct copy_page_info {
+	struct work_struct copy_page_work;
+	char *to;
+	char *from;
+	unsigned long chunk_size;
+};
+
+static void exchange_page_routine(char *to, char *from, unsigned long chunk_size)
+{
+	u64 tmp;
+	int i;
+
+	for (i = 0; i < chunk_size; i += sizeof(tmp)) {
+		tmp = *((u64*)(from + i));
+		*((u64*)(from + i)) = *((u64*)(to + i));
+		*((u64*)(to + i)) = tmp;
+	}
+}
+
+static void exchange_page_work_queue_thread(struct work_struct *work)
+{
+	struct copy_page_info *my_work = (struct copy_page_info*)work;
+
+	exchange_page_routine(my_work->to,
+							  my_work->from,
+							  my_work->chunk_size);
+}
+
+int exchange_page_mthread(struct page *to, struct page *from, int nr_pages)
+{
+	int total_mt_num = limit_mt_num;
+	int to_node = page_to_nid(to);
+	int i;
+	struct copy_page_info *work_items;
+	char *vto, *vfrom;
+	unsigned long chunk_size;
+	const struct cpumask *per_node_cpumask = cpumask_of_node(to_node);
+	int cpu_id_list[32] = {0};
+	int cpu;
+
+	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 > 32 || total_mt_num < 1)
+		return -ENODEV;
+
+	work_items = kvzalloc(sizeof(struct copy_page_info)*total_mt_num,
+						 GFP_KERNEL);
+	if (!work_items)
+		return -ENOMEM;
+
+	i = 0;
+	for_each_cpu(cpu, per_node_cpumask) {
+		if (i >= total_mt_num)
+			break;
+		cpu_id_list[i] = cpu;
+		++i;
+	}
+
+	/* XXX: assume no highmem  */
+	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],
+				exchange_page_work_queue_thread);
+
+		work_items[i].to = vto + i * chunk_size;
+		work_items[i].from = vfrom + i * chunk_size;
+		work_items[i].chunk_size = chunk_size;
+
+		queue_work_on(cpu_id_list[i],
+					  system_highpri_wq,
+					  (struct work_struct *)&work_items[i]);
+	}
+
+	/* Wait until it finishes  */
+	flush_workqueue(system_highpri_wq);
+
+	kunmap(to);
+	kunmap(from);
+
+	kvfree(work_items);
+
+	return 0;
+}
+
+int exchange_page_lists_mthread(struct page **to, struct page **from, int nr_pages)
+{
+	int err = 0;
+	unsigned int total_mt_num = limit_mt_num;
+	int to_node = page_to_nid(*to);
+	int i;
+	struct copy_page_info *work_items;
+	int nr_pages_per_page = hpage_nr_pages(*from);
+	const struct cpumask *per_node_cpumask = cpumask_of_node(to_node);
+	int cpu_id_list[32] = {0};
+	int cpu;
+	int item_idx;
+
+
+	total_mt_num = min_t(unsigned int, total_mt_num,
+						 cpumask_weight(per_node_cpumask));
+
+	if (total_mt_num > 32 || total_mt_num < 1)
+		return -ENODEV;
+
+	if (nr_pages < total_mt_num) {
+		int residual_nr_pages = nr_pages - rounddown_pow_of_two(nr_pages);
+
+		if (residual_nr_pages) {
+			for (i = 0; i < residual_nr_pages; ++i) {
+				BUG_ON(hpage_nr_pages(to[i]) != hpage_nr_pages(from[i]));
+				err = exchange_page_mthread(to[i], from[i], hpage_nr_pages(to[i]));
+				VM_BUG_ON(err);
+			}
+			nr_pages = rounddown_pow_of_two(nr_pages);
+			to = &to[residual_nr_pages];
+			from = &from[residual_nr_pages];
+		}
+
+		work_items = kvzalloc(sizeof(struct copy_page_info)*total_mt_num,
+							 GFP_KERNEL);
+	} else
+		work_items = kvzalloc(sizeof(struct copy_page_info)*nr_pages,
+							 GFP_KERNEL);
+	if (!work_items)
+		return -ENOMEM;
+
+	i = 0;
+	for_each_cpu(cpu, per_node_cpumask) {
+		if (i >= total_mt_num)
+			break;
+		cpu_id_list[i] = cpu;
+		++i;
+	}
+
+	if (nr_pages < total_mt_num) {
+		for (cpu = 0; cpu < total_mt_num; ++cpu)
+			INIT_WORK((struct work_struct *)&work_items[cpu],
+					  exchange_page_work_queue_thread);
+		cpu = 0;
+		for (item_idx = 0; item_idx < nr_pages; ++item_idx) {
+			unsigned long chunk_size = nr_pages * PAGE_SIZE * hpage_nr_pages(from[item_idx]) / total_mt_num;
+			char *vfrom = kmap(from[item_idx]);
+			char *vto = kmap(to[item_idx]);
+			VM_BUG_ON(PAGE_SIZE * hpage_nr_pages(from[item_idx]) % total_mt_num);
+			VM_BUG_ON(total_mt_num % nr_pages);
+			BUG_ON(hpage_nr_pages(to[item_idx]) !=
+				   hpage_nr_pages(from[item_idx]));
+
+			for (i = 0; i < (total_mt_num/nr_pages); ++cpu, ++i) {
+				work_items[cpu].to = vto + chunk_size * i;
+				work_items[cpu].from = vfrom + chunk_size * i;
+				work_items[cpu].chunk_size = chunk_size;
+			}
+		}
+		if (cpu != total_mt_num)
+			pr_err("%s: only %d out of %d pages are transferred\n", __func__,
+				cpu - 1, total_mt_num);
+
+		for (cpu = 0; cpu < total_mt_num; ++cpu)
+			queue_work_on(cpu_id_list[cpu],
+						  system_highpri_wq,
+						  (struct work_struct *)&work_items[cpu]);
+	} else {
+		for (i = 0; i < nr_pages; ++i) {
+			int thread_idx = i % total_mt_num;
+
+			INIT_WORK((struct work_struct *)&work_items[i], exchange_page_work_queue_thread);
+
+			/* XXX: assume no highmem  */
+			work_items[i].to = kmap(to[i]);
+			work_items[i].from = kmap(from[i]);
+			work_items[i].chunk_size = PAGE_SIZE * hpage_nr_pages(from[i]);
+
+			BUG_ON(hpage_nr_pages(to[i]) != hpage_nr_pages(from[i]));
+
+			queue_work_on(cpu_id_list[thread_idx], system_highpri_wq, (struct work_struct *)&work_items[i]);
+		}
+	}
+
+	/* Wait until it finishes  */
+	flush_workqueue(system_highpri_wq);
+
+	for (i = 0; i < nr_pages; ++i) {
+			kunmap(to[i]);
+			kunmap(from[i]);
+	}
+
+	kvfree(work_items);
+
+	return err;
+}
+
diff --git a/mm/internal.h b/mm/internal.h
index 51f5e1b..a039459 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -561,4 +561,9 @@ extern int copy_page_lists_dma_always(struct page **to,
 extern int copy_page_lists_mt(struct page **to,
 			struct page **from, int nr_pages);
 
+extern int exchange_page_mthread(struct page *to, struct page *from,
+			int nr_pages);
+extern int exchange_page_lists_mthread(struct page **to,
+						  struct page **from, 
+						  int nr_pages);
 #endif	/* __MM_INTERNAL_H */
-- 
2.7.4