f2fs: add ckpt_thread_ioprio sysfs node

Added "ckpt_thread_ioprio" sysfs node to give a way to change checkpoint
merge daemon's io priority. Its default value is "be,3", which means
"BE" I/O class and I/O priority "3". We can select the class between "rt"
and "be", and set the I/O priority within valid range of it.
"," delimiter is necessary in between I/O class and priority number.
Signed-off-by: Daeho Jeong <daehojeong@google.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

Documentation/ABI/testing/sysfs-fs-f2fs

@@ -400,3 +400,12 @@ Description:	Show status of f2fs superblock in real time.
 		0x1000 SBI_QUOTA_NEED_REPAIR quota file may be corrupted
 		0x2000 SBI_IS_RESIZEFS       resizefs is in process
 		====== ===================== =================================
+
+What:		/sys/fs/f2fs/<disk>/ckpt_thread_ioprio
+Date:		January 2021
+Contact:	"Daeho Jeong" <daehojeong@google.com>
+Description:	Give a way to change checkpoint merge daemon's io priority.
+		Its default value is "be,3", which means "BE" I/O class and
+		I/O priority "3". We can select the class between "rt" and "be",
+		and set the I/O priority within valid range of it. "," delimiter
+		is necessary in between I/O class and priority number.

fs/f2fs/checkpoint.c

@@ -1851,7 +1851,7 @@ int f2fs_start_ckpt_thread(struct f2fs_sb_info *sbi)
 		return -ENOMEM;
 	}
 
-	set_task_ioprio(cprc->f2fs_issue_ckpt, DEFAULT_CHECKPOINT_IOPRIO);
+	set_task_ioprio(cprc->f2fs_issue_ckpt, cprc->ckpt_thread_ioprio);
 
 	return 0;
 }
@@ -1877,6 +1877,7 @@ void f2fs_init_ckpt_req_control(struct f2fs_sb_info *sbi)
 	atomic_set(&cprc->issued_ckpt, 0);
 	atomic_set(&cprc->total_ckpt, 0);
 	atomic_set(&cprc->queued_ckpt, 0);
+	cprc->ckpt_thread_ioprio = DEFAULT_CHECKPOINT_IOPRIO;
 	init_waitqueue_head(&cprc->ckpt_wait_queue);
 	init_llist_head(&cprc->issue_list);
 	spin_lock_init(&cprc->stat_lock);

fs/f2fs/f2fs.h

@@ -277,6 +277,7 @@ struct ckpt_req {
 
 struct ckpt_req_control {
 	struct task_struct *f2fs_issue_ckpt;	/* checkpoint task */
+	int ckpt_thread_ioprio;			/* checkpoint merge thread ioprio */
 	wait_queue_head_t ckpt_wait_queue;	/* waiting queue for wake-up */
 	atomic_t issued_ckpt;		/* # of actually issued ckpts */
 	atomic_t total_ckpt;		/* # of total ckpts */

fs/f2fs/sysfs.c

@@ -11,6 +11,7 @@
 #include <linux/f2fs_fs.h>
 #include <linux/seq_file.h>
 #include <linux/unicode.h>
+#include <linux/ioprio.h>
 
 #include "f2fs.h"
 #include "segment.h"
@@ -34,6 +35,7 @@ enum {
 	FAULT_INFO_TYPE,	/* struct f2fs_fault_info */
 #endif
 	RESERVED_BLOCKS,	/* struct f2fs_sb_info */
+	CPRC_INFO,	/* struct ckpt_req_control */
 };
 
 struct f2fs_attr {
@@ -70,6 +72,8 @@ static unsigned char *__struct_ptr(struct f2fs_sb_info *sbi, int struct_type)
 	else if (struct_type == STAT_INFO)
 		return (unsigned char *)F2FS_STAT(sbi);
 #endif
+	else if (struct_type == CPRC_INFO)
+		return (unsigned char *)&sbi->cprc_info;
 	return NULL;
 }
 
@@ -261,6 +265,23 @@ static ssize_t f2fs_sbi_show(struct f2fs_attr *a,
 		return len;
 	}
 
+	if (!strcmp(a->attr.name, "ckpt_thread_ioprio")) {
+		struct ckpt_req_control *cprc = &sbi->cprc_info;
+		int len = 0;
+		int class = IOPRIO_PRIO_CLASS(cprc->ckpt_thread_ioprio);
+		int data = IOPRIO_PRIO_DATA(cprc->ckpt_thread_ioprio);
+
+		if (class == IOPRIO_CLASS_RT)
+			len += scnprintf(buf + len, PAGE_SIZE - len, "rt,");
+		else if (class == IOPRIO_CLASS_BE)
+			len += scnprintf(buf + len, PAGE_SIZE - len, "be,");
+		else
+			return -EINVAL;
+
+		len += scnprintf(buf + len, PAGE_SIZE - len, "%d\n", data);
+		return len;
+	}
+
 	ui = (unsigned int *)(ptr + a->offset);
 
 	return sprintf(buf, "%u\n", *ui);
@@ -314,6 +335,38 @@ static ssize_t __sbi_store(struct f2fs_attr *a,
 		return ret ? ret : count;
 	}
 
+	if (!strcmp(a->attr.name, "ckpt_thread_ioprio")) {
+		const char *name = strim((char *)buf);
+		struct ckpt_req_control *cprc = &sbi->cprc_info;
+		int class;
+		long data;
+		int ret;
+
+		if (!strncmp(name, "rt,", 3))
+			class = IOPRIO_CLASS_RT;
+		else if (!strncmp(name, "be,", 3))
+			class = IOPRIO_CLASS_BE;
+		else
+			return -EINVAL;
+
+		name += 3;
+		ret = kstrtol(name, 10, &data);
+		if (ret)
+			return ret;
+		if (data >= IOPRIO_BE_NR || data < 0)
+			return -EINVAL;
+
+		cprc->ckpt_thread_ioprio = IOPRIO_PRIO_VALUE(class, data);
+		if (test_opt(sbi, MERGE_CHECKPOINT)) {
+			ret = set_task_ioprio(cprc->f2fs_issue_ckpt,
+					cprc->ckpt_thread_ioprio);
+			if (ret)
+				return ret;
+		}
+
+		return count;
+	}
+
 	ui = (unsigned int *)(ptr + a->offset);
 
 	ret = kstrtoul(skip_spaces(buf), 0, &t);
@@ -573,6 +626,7 @@ F2FS_RW_ATTR(FAULT_INFO_TYPE, f2fs_fault_info, inject_type, inject_type);
 #endif
 F2FS_RW_ATTR(F2FS_SBI, f2fs_sb_info, data_io_flag, data_io_flag);
 F2FS_RW_ATTR(F2FS_SBI, f2fs_sb_info, node_io_flag, node_io_flag);
+F2FS_RW_ATTR(CPRC_INFO, ckpt_req_control, ckpt_thread_ioprio, ckpt_thread_ioprio);
 F2FS_GENERAL_RO_ATTR(dirty_segments);
 F2FS_GENERAL_RO_ATTR(free_segments);
 F2FS_GENERAL_RO_ATTR(lifetime_write_kbytes);
@@ -658,6 +712,7 @@ static struct attribute *f2fs_attrs[] = {
 #endif
 	ATTR_LIST(data_io_flag),
 	ATTR_LIST(node_io_flag),
+	ATTR_LIST(ckpt_thread_ioprio),
 	ATTR_LIST(dirty_segments),
 	ATTR_LIST(free_segments),
 	ATTR_LIST(unusable),