I think the aim of reserved_blocks function is to leave space for f2fs and FTL, so I change it to a soft version so that it can be used to fit to the data image which does not satisfy the hard version, especially for backward compatibility when updated kernel with new default reserved_blocks set (currently it is initially set 0 as default, but can be set any value with my new patch).

As for the uid/gid, does current f2fs space management design consider this issue? IMO, I think we can just ensure the reserved space for file system no matter user/system type. Whether the value of reserved_blocks is OK or not, should not be filesystem's issue. Filesystem just provide this interface, and the upper layer, such as android vold should take care of the value of reserved_blocks and make sure its value is appropriate and will not block any activation of system user, if it really happens, android should change the value dynamically, it is fine, since we make reserved_blocks to a soft version.

On 2017/8/10 11:15, Chao Yu wrote:
On 2017/8/8 21:43, Yunlong Song wrote:
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.
Oh, this looks like a soft limitation in quota system, but original
reserved_blocks implementation likes a hard one, so this patch changes the
semantics of reserved_blocks.

Actually, I doubt that it would be hard to reserve all left free space in real
user scenario now, since system user's activation may depend on free space of
data partition due to file creation requirement, so w/o supporting feature of
uid/gid reserved block, soft reservation will block any activation of system
user, such as android.

Thanks,

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,
  };

.


--
Thanks,
Yunlong Song


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