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.

Signed-off-by: Yunlong Song <yunlong.s...@huawei.com>
---
 Documentation/ABI/testing/sysfs-fs-f2fs |  6 ++++++
 fs/f2fs/f2fs.h                          |  9 +++++++--
 fs/f2fs/super.c                         |  4 +++-
 fs/f2fs/sysfs.c                         | 15 ++++++++++-----
 4 files changed, 26 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" <jaeg...@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.s...@huawei.com>
+Description:
+                Shows current reserved blocks in system.
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index cea329f..3b7056f 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -1040,6 +1040,7 @@ 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 */
 
@@ -1514,7 +1515,7 @@ 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;
@@ -1548,6 +1549,8 @@ 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);
 }
@@ -1694,7 +1697,7 @@ 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;
@@ -1737,6 +1740,8 @@ 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..2934aa2 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 +2411,8 @@ 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 = min(sbi->reserved_blocks,
+                                               sbi->user_block_count - 
sbi->total_valid_block_count);
 
        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 b769a3d..405c13f 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;
+               sbi->cur_reserved_blocks = min(t, sbi->user_block_count -
+                                                                               
sbi->total_valid_block_count);
                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

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