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Date: Tue, 7 Jun 2011 18:07:48 +0300
From: amir73il@...rs.sourceforge.net
To: linux-ext4@...r.kernel.org
Cc: tytso@....edu, lczerner@...hat.com,
Amir Goldstein <amir73il@...rs.sf.net>,
Yongqiang Yang <xiaoqiangnk@...il.com>
Subject: [PATCH v1 21/36] ext4: snapshot control - reserve disk space for snapshot
From: Amir Goldstein <amir73il@...rs.sf.net>
Ensure there is enough disk space for snapshot file future use.
Reserve disk space on snapshot take based on file system overhead
size, number of directories and number of blocks/inodes in use.
Signed-off-by: Amir Goldstein <amir73il@...rs.sf.net>
Signed-off-by: Yongqiang Yang <xiaoqiangnk@...il.com>
---
fs/ext4/balloc.c | 25 +++++++++++++++++++++++++
fs/ext4/ext4.h | 2 ++
fs/ext4/mballoc.c | 6 ++++++
fs/ext4/snapshot_ctl.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
fs/ext4/super.c | 16 +++++++++++++++-
5 files changed, 92 insertions(+), 1 deletions(-)
diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
index 8f1803f..1c140e4 100644
--- a/fs/ext4/balloc.c
+++ b/fs/ext4/balloc.c
@@ -372,6 +372,8 @@ ext4_read_block_bitmap(struct super_block *sb, ext4_group_t block_group)
static int ext4_has_free_blocks(struct ext4_sb_info *sbi, s64 nblocks)
{
s64 free_blocks, dirty_blocks, root_blocks;
+ ext4_fsblk_t snapshot_r_blocks;
+ handle_t *handle = journal_current_handle();
struct percpu_counter *fbc = &sbi->s_freeblocks_counter;
struct percpu_counter *dbc = &sbi->s_dirtyblocks_counter;
@@ -379,6 +381,29 @@ static int ext4_has_free_blocks(struct ext4_sb_info *sbi, s64 nblocks)
dirty_blocks = percpu_counter_read_positive(dbc);
root_blocks = ext4_r_blocks_count(sbi->s_es);
+ if (ext4_snapshot_active(sbi)) {
+ if (unlikely(free_blocks < (nblocks + dirty_blocks)))
+ /* sorry, but we're really out of space */
+ return 0;
+ if (handle && unlikely(IS_COWING(handle)))
+ /* any available space may be used by COWing task */
+ return 1;
+ /* reserve blocks for active snapshot */
+ snapshot_r_blocks =
+ le64_to_cpu(sbi->s_es->s_snapshot_r_blocks_count);
+ /*
+ * The last snapshot_r_blocks are reserved for active snapshot
+ * and may not be allocated even by root.
+ */
+ if (free_blocks < (nblocks + dirty_blocks + snapshot_r_blocks))
+ return 0;
+ /*
+ * Mortal users must reserve blocks for both snapshot and
+ * root user.
+ */
+ root_blocks += snapshot_r_blocks;
+ }
+
if (free_blocks - (nblocks + root_blocks + dirty_blocks) <
EXT4_FREEBLOCKS_WATERMARK) {
free_blocks = percpu_counter_sum_positive(fbc);
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 198d7d4..8d82125 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1963,6 +1963,8 @@ extern __le16 ext4_group_desc_csum(struct ext4_sb_info *sbi, __u32 group,
struct ext4_group_desc *gdp);
extern int ext4_group_desc_csum_verify(struct ext4_sb_info *sbi, __u32 group,
struct ext4_group_desc *gdp);
+struct kstatfs;
+extern int ext4_statfs_sb(struct super_block *sb, struct kstatfs *buf);
static inline ext4_fsblk_t ext4_blocks_count(struct ext4_super_block *es)
{
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 6e4d960..899c12c 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -4296,10 +4296,16 @@ ext4_fsblk_t ext4_mb_new_blocks(handle_t *handle,
return 0;
}
reserv_blks = ar->len;
+ if (unlikely(ar->flags & EXT4_MB_HINT_COWING)) {
+ /* don't fail when allocating blocks for COW */
+ dquot_alloc_block_nofail(ar->inode, ar->len);
+ goto nofail;
+ }
while (ar->len && dquot_alloc_block(ar->inode, ar->len)) {
ar->flags |= EXT4_MB_HINT_NOPREALLOC;
ar->len--;
}
+nofail:
inquota = ar->len;
if (ar->len == 0) {
*errp = -EDQUOT;
diff --git a/fs/ext4/snapshot_ctl.c b/fs/ext4/snapshot_ctl.c
index 360581d..a610025 100644
--- a/fs/ext4/snapshot_ctl.c
+++ b/fs/ext4/snapshot_ctl.c
@@ -711,6 +711,8 @@ int ext4_snapshot_take(struct inode *inode)
int fixing = 0;
int i;
int err = -EIO;
+ u64 snapshot_r_blocks;
+ struct kstatfs statfs;
if (!sbi->s_sbh)
goto out_err;
@@ -739,6 +741,47 @@ int ext4_snapshot_take(struct inode *inode)
}
err = -EIO;
+ /* update fs statistics to calculate snapshot reserved space */
+ if (ext4_statfs_sb(sb, &statfs)) {
+ snapshot_debug(1, "failed to statfs before snapshot (%u) "
+ "take\n", inode->i_generation);
+ goto out_err;
+ }
+ /*
+ * Estimate maximum disk space for snapshot file metadata based on:
+ * 1 indirect block per 1K fs blocks (to map moved data blocks)
+ * +1 data block per 1K fs blocks (to copy indirect blocks)
+ * +1 data block per fs meta block (to copy meta blocks)
+ * +1 data block per directory (to copy small directory index blocks)
+ * +1 data block per X inodes (to copy large directory index blocks)
+ *
+ * We estimate no. of dir blocks from no. of allocated inode, assuming
+ * an avg. dir record size of 64 bytes. This assumption can break in
+ * 2 cases:
+ * 1. long file names (in avg.)
+ * 2. large no. of hard links (many dir records for the same inode)
+ *
+ * Under estimation can lead to potential ENOSPC during COW, which
+ * will trigger an ext4_error(). Hopefully, error behavior is set to
+ * remount-ro, so snapshot will not be corrupted.
+ *
+ * XXX: reserved space may be too small in data jounaling mode,
+ * which is currently not supported.
+ */
+#define AVG_DIR_RECORD_SIZE_BITS 6 /* 64 bytes */
+#define AVG_INODES_PER_DIR_BLOCK \
+ (SNAPSHOT_BLOCK_SIZE_BITS - AVG_DIR_RECORD_SIZE_BITS)
+ snapshot_r_blocks = 2 * (statfs.f_blocks >>
+ SNAPSHOT_ADDR_PER_BLOCK_BITS) +
+ statfs.f_spare[0] + statfs.f_spare[1] +
+ ((statfs.f_files - statfs.f_ffree) >>
+ AVG_INODES_PER_DIR_BLOCK);
+
+ /* verify enough free space before taking the snapshot */
+ if (statfs.f_bfree < snapshot_r_blocks) {
+ err = -ENOSPC;
+ goto out_err;
+ }
/*
* flush journal to disk and clear the RECOVER flag
@@ -876,6 +919,7 @@ next_inode:
goto out_unlockfs;
/* set as on-disk active snapshot */
+ sbi->s_es->s_snapshot_r_blocks_count = cpu_to_le64(snapshot_r_blocks);
sbi->s_es->s_snapshot_id =
cpu_to_le32(le32_to_cpu(sbi->s_es->s_snapshot_id) + 1);
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index dbe5651..a7be485 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -4515,7 +4515,11 @@ restore_opts:
static int ext4_statfs(struct dentry *dentry, struct kstatfs *buf)
{
- struct super_block *sb = dentry->d_sb;
+ return ext4_statfs_sb(dentry->d_sb, buf);
+}
+
+int ext4_statfs_sb(struct super_block *sb, struct kstatfs *buf)
+{
struct ext4_sb_info *sbi = EXT4_SB(sb);
struct ext4_super_block *es = sbi->s_es;
u64 fsid;
@@ -4567,6 +4571,16 @@ static int ext4_statfs(struct dentry *dentry, struct kstatfs *buf)
buf->f_bavail = buf->f_bfree - ext4_r_blocks_count(es);
if (buf->f_bfree < ext4_r_blocks_count(es))
buf->f_bavail = 0;
+ if (ext4_snapshot_active(sbi)) {
+ if (buf->f_bfree < ext4_r_blocks_count(es) +
+ le64_to_cpu(es->s_snapshot_r_blocks_count))
+ buf->f_bavail = 0;
+ else
+ buf->f_bavail -=
+ le64_to_cpu(es->s_snapshot_r_blocks_count);
+ }
+ buf->f_spare[0] = percpu_counter_sum_positive(&sbi->s_dirs_counter);
+ buf->f_spare[1] = sbi->s_overhead_last;
buf->f_files = le32_to_cpu(es->s_inodes_count);
buf->f_ffree = percpu_counter_sum_positive(&sbi->s_freeinodes_counter);
buf->f_namelen = EXT4_NAME_LEN;
--
1.7.4.1
--
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