[PATCH v2] f2fs: introduce cur_reserved_blocks in sysfs

[Yunlong Song <yunlong.song@huawei.com>]

In this patch, we add a new sysfs interface, we can use it to gradually achieve
the reserved_blocks finally, even when reserved_blocks is initially set over
user_block_count - total_valid_block_count. This is very useful, especially when
we upgrade kernel with new reserved_blocks value, but old disk image unluckily has
user_block_count - total_valid_block_count smaller than the desired reserved_blocks.
With this patch, f2fs can try its best to reserve space and get close to the
reserved_blocks, and the current value of achieved reserved_blocks can be shown
in real time.

To ensure there is enough space for supporting system's activation, we safely
increase cur_reserved_blocks in dev_valid_block(,node)_count to only take up the
blocks which are just obsoleted.

Signed-off-by: Yunlong Song <yunlong.song@huawei.com>
---
 Documentation/ABI/testing/sysfs-fs-f2fs |  6 ++++++
 fs/f2fs/f2fs.h                          |  9 +++++++--
 fs/f2fs/super.c                         |  3 ++-
 fs/f2fs/sysfs.c                         | 15 ++++++++++-----
 4 files changed, 25 insertions(+), 8 deletions(-)

diff --git a/Documentation/ABI/testing/sysfs-fs-f2fs b/Documentation/ABI/testing/sysfs-fs-f2fs
index 11b7f4e..bdbb9f3 100644
--- a/Documentation/ABI/testing/sysfs-fs-f2fs
+++ b/Documentation/ABI/testing/sysfs-fs-f2fs
@@ -151,3 +151,9 @@ Date:		August 2017
 Contact:	"Jaegeuk Kim" <jaegeuk@kernel.org>
 Description:
 		 Controls sleep time of GC urgent mode
+
+What:		/sys/fs/f2fs/<disk>/cur_reserved_blocks
+Date:		August 2017
+Contact:	"Yunlong Song" <yunlong.song@huawei.com>
+Description:
+		 Shows current reserved blocks in system.
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 2f20b6b..62d7343 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -1041,6 +1041,7 @@ struct f2fs_sb_info {
 	block_t discard_blks;			/* discard command candidats */
 	block_t last_valid_block_count;		/* for recovery */
 	block_t reserved_blocks;		/* configurable reserved blocks */
+	block_t cur_reserved_blocks;		/* current reserved blocks */
 
 	u32 s_next_generation;			/* for NFS support */
 
@@ -1515,7 +1516,7 @@ static inline int inc_valid_block_count(struct f2fs_sb_info *sbi,
 
 	spin_lock(&sbi->stat_lock);
 	sbi->total_valid_block_count += (block_t)(*count);
-	avail_user_block_count = sbi->user_block_count - sbi->reserved_blocks;
+	avail_user_block_count = sbi->user_block_count - sbi->cur_reserved_blocks;
 	if (unlikely(sbi->total_valid_block_count > avail_user_block_count)) {
 		diff = sbi->total_valid_block_count - avail_user_block_count;
 		*count -= diff;
@@ -1549,6 +1550,8 @@ static inline void dec_valid_block_count(struct f2fs_sb_info *sbi,
 	f2fs_bug_on(sbi, sbi->total_valid_block_count < (block_t) count);
 	f2fs_bug_on(sbi, inode->i_blocks < sectors);
 	sbi->total_valid_block_count -= (block_t)count;
+	sbi->cur_reserved_blocks = min(sbi->reserved_blocks,
+									sbi->cur_reserved_blocks + count);
 	spin_unlock(&sbi->stat_lock);
 	f2fs_i_blocks_write(inode, count, false, true);
 }
@@ -1695,7 +1698,7 @@ static inline int inc_valid_node_count(struct f2fs_sb_info *sbi,
 	spin_lock(&sbi->stat_lock);
 
 	valid_block_count = sbi->total_valid_block_count + 1;
-	if (unlikely(valid_block_count + sbi->reserved_blocks >
+	if (unlikely(valid_block_count + sbi->cur_reserved_blocks >
 						sbi->user_block_count)) {
 		spin_unlock(&sbi->stat_lock);
 		goto enospc;
@@ -1738,6 +1741,8 @@ static inline void dec_valid_node_count(struct f2fs_sb_info *sbi,
 
 	sbi->total_valid_node_count--;
 	sbi->total_valid_block_count--;
+	sbi->cur_reserved_blocks = min(sbi->reserved_blocks,
+									sbi->cur_reserved_blocks + 1);
 
 	spin_unlock(&sbi->stat_lock);
 
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index 4c1bdcb..16a805f 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -957,7 +957,7 @@ static int f2fs_statfs(struct dentry *dentry, struct kstatfs *buf)
 	buf->f_blocks = total_count - start_count;
 	buf->f_bfree = user_block_count - valid_user_blocks(sbi) + ovp_count;
 	buf->f_bavail = user_block_count - valid_user_blocks(sbi) -
-						sbi->reserved_blocks;
+						sbi->cur_reserved_blocks;
 
 	avail_node_count = sbi->total_node_count - F2FS_RESERVED_NODE_NUM;
 
@@ -2411,6 +2411,7 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
 				le64_to_cpu(sbi->ckpt->valid_block_count);
 	sbi->last_valid_block_count = sbi->total_valid_block_count;
 	sbi->reserved_blocks = 0;
+	sbi->cur_reserved_blocks = 0;
 
 	for (i = 0; i < NR_INODE_TYPE; i++) {
 		INIT_LIST_HEAD(&sbi->inode_list[i]);
diff --git a/fs/f2fs/sysfs.c b/fs/f2fs/sysfs.c
index a1be5ac..03f9d3d 100644
--- a/fs/f2fs/sysfs.c
+++ b/fs/f2fs/sysfs.c
@@ -76,6 +76,12 @@ static ssize_t lifetime_write_kbytes_show(struct f2fs_attr *a,
 			BD_PART_WRITTEN(sbi)));
 }
 
+static ssize_t cur_reserved_blocks_show(struct f2fs_attr *a,
+		struct f2fs_sb_info *sbi, char *buf)
+{
+	return snprintf(buf, PAGE_SIZE, "%u\n", sbi->cur_reserved_blocks);
+}
+
 static ssize_t features_show(struct f2fs_attr *a,
 		struct f2fs_sb_info *sbi, char *buf)
 {
@@ -143,12 +149,9 @@ static ssize_t f2fs_sbi_store(struct f2fs_attr *a,
 #endif
 	if (a->struct_type == RESERVED_BLOCKS) {
 		spin_lock(&sbi->stat_lock);
-		if ((unsigned long)sbi->total_valid_block_count + t >
-				(unsigned long)sbi->user_block_count) {
-			spin_unlock(&sbi->stat_lock);
-			return -EINVAL;
-		}
 		*ui = t;
+		if (t < sbi->cur_reserved_blocks)
+			sbi->cur_reserved_blocks = t;
 		spin_unlock(&sbi->stat_lock);
 		return count;
 	}
@@ -274,6 +277,7 @@ static ssize_t f2fs_feature_show(struct f2fs_attr *a,
 #endif
 F2FS_GENERAL_RO_ATTR(lifetime_write_kbytes);
 F2FS_GENERAL_RO_ATTR(features);
+F2FS_GENERAL_RO_ATTR(cur_reserved_blocks);
 
 #ifdef CONFIG_F2FS_FS_ENCRYPTION
 F2FS_FEATURE_RO_ATTR(encryption, FEAT_CRYPTO);
@@ -317,6 +321,7 @@ static ssize_t f2fs_feature_show(struct f2fs_attr *a,
 	ATTR_LIST(lifetime_write_kbytes),
 	ATTR_LIST(features),
 	ATTR_LIST(reserved_blocks),
+	ATTR_LIST(cur_reserved_blocks),
 	NULL,
 };
 
-- 
1.8.5.2