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authorWang Xiaoguang <wangxg.fnst@cn.fujitsu.com>2016-07-25 15:51:40 +0800
committerChris Mason <clm@fb.com>2016-08-25 03:58:26 -0700
commit18513091af9483ba84328d42092bd4d42a3c958f (patch)
treee5a8dfa241105b399c110cc4f79400b332136272 /fs/btrfs/file.c
parent4824f1f412f75e9f84b9cecbde828e8f4699f82d (diff)
btrfs: update btrfs_space_info's bytes_may_use timely
This patch can fix some false ENOSPC errors, below test script can reproduce one false ENOSPC error: #!/bin/bash dd if=/dev/zero of=fs.img bs=$((1024*1024)) count=128 dev=$(losetup --show -f fs.img) mkfs.btrfs -f -M $dev mkdir /tmp/mntpoint mount $dev /tmp/mntpoint cd /tmp/mntpoint xfs_io -f -c "falloc 0 $((64*1024*1024))" testfile Above script will fail for ENOSPC reason, but indeed fs still has free space to satisfy this request. Please see call graph: btrfs_fallocate() |-> btrfs_alloc_data_chunk_ondemand() | bytes_may_use += 64M |-> btrfs_prealloc_file_range() |-> btrfs_reserve_extent() |-> btrfs_add_reserved_bytes() | alloc_type is RESERVE_ALLOC_NO_ACCOUNT, so it does not | change bytes_may_use, and bytes_reserved += 64M. Now | bytes_may_use + bytes_reserved == 128M, which is greater | than btrfs_space_info's total_bytes, false enospc occurs. | Note, the bytes_may_use decrease operation will be done in | end of btrfs_fallocate(), which is too late. Here is another simple case for buffered write: CPU 1 | CPU 2 | |-> cow_file_range() |-> __btrfs_buffered_write() |-> btrfs_reserve_extent() | | | | | | | | | ..... | |-> btrfs_check_data_free_space() | | | | |-> extent_clear_unlock_delalloc() | In CPU 1, btrfs_reserve_extent()->find_free_extent()-> btrfs_add_reserved_bytes() do not decrease bytes_may_use, the decrease operation will be delayed to be done in extent_clear_unlock_delalloc(). Assume in this case, btrfs_reserve_extent() reserved 128MB data, CPU2's btrfs_check_data_free_space() tries to reserve 100MB data space. If 100MB > data_sinfo->total_bytes - data_sinfo->bytes_used - data_sinfo->bytes_reserved - data_sinfo->bytes_pinned - data_sinfo->bytes_readonly - data_sinfo->bytes_may_use btrfs_check_data_free_space() will try to allcate new data chunk or call btrfs_start_delalloc_roots(), or commit current transaction in order to reserve some free space, obviously a lot of work. But indeed it's not necessary as long as decreasing bytes_may_use timely, we still have free space, decreasing 128M from bytes_may_use. To fix this issue, this patch chooses to update bytes_may_use for both data and metadata in btrfs_add_reserved_bytes(). For compress path, real extent length may not be equal to file content length, so introduce a ram_bytes argument for btrfs_reserve_extent(), find_free_extent() and btrfs_add_reserved_bytes(), it's becasue bytes_may_use is increased by file content length. Then compress path can update bytes_may_use correctly. Also now we can discard RESERVE_ALLOC_NO_ACCOUNT, RESERVE_ALLOC and RESERVE_FREE. As we know, usually EXTENT_DO_ACCOUNTING is used for error path. In run_delalloc_nocow(), for inode marked as NODATACOW or extent marked as PREALLOC, we also need to update bytes_may_use, but can not pass EXTENT_DO_ACCOUNTING, because it also clears metadata reservation, so here we introduce EXTENT_CLEAR_DATA_RESV flag to indicate btrfs_clear_bit_hook() to update btrfs_space_info's bytes_may_use. Meanwhile __btrfs_prealloc_file_range() will call btrfs_free_reserved_data_space() internally for both sucessful and failed path, btrfs_prealloc_file_range()'s callers does not need to call btrfs_free_reserved_data_space() any more. Signed-off-by: Wang Xiaoguang <wangxg.fnst@cn.fujitsu.com> Reviewed-by: Josef Bacik <jbacik@fb.com> Signed-off-by: David Sterba <dsterba@suse.com> Signed-off-by: Chris Mason <clm@fb.com>
Diffstat (limited to 'fs/btrfs/file.c')
-rw-r--r--fs/btrfs/file.c26
1 files changed, 15 insertions, 11 deletions
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 5842423f8f47..3391f2adf0c8 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -2675,6 +2675,7 @@ static long btrfs_fallocate(struct file *file, int mode,
alloc_start = round_down(offset, blocksize);
alloc_end = round_up(offset + len, blocksize);
+ cur_offset = alloc_start;
/* Make sure we aren't being give some crap mode */
if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE))
@@ -2767,7 +2768,6 @@ static long btrfs_fallocate(struct file *file, int mode,
/* First, check if we exceed the qgroup limit */
INIT_LIST_HEAD(&reserve_list);
- cur_offset = alloc_start;
while (1) {
em = btrfs_get_extent(inode, NULL, 0, cur_offset,
alloc_end - cur_offset, 0);
@@ -2794,6 +2794,14 @@ static long btrfs_fallocate(struct file *file, int mode,
last_byte - cur_offset);
if (ret < 0)
break;
+ } else {
+ /*
+ * Do not need to reserve unwritten extent for this
+ * range, free reserved data space first, otherwise
+ * it'll result in false ENOSPC error.
+ */
+ btrfs_free_reserved_data_space(inode, cur_offset,
+ last_byte - cur_offset);
}
free_extent_map(em);
cur_offset = last_byte;
@@ -2811,6 +2819,9 @@ static long btrfs_fallocate(struct file *file, int mode,
range->start,
range->len, 1 << inode->i_blkbits,
offset + len, &alloc_hint);
+ else
+ btrfs_free_reserved_data_space(inode, range->start,
+ range->len);
list_del(&range->list);
kfree(range);
}
@@ -2845,18 +2856,11 @@ out_unlock:
unlock_extent_cached(&BTRFS_I(inode)->io_tree, alloc_start, locked_end,
&cached_state, GFP_KERNEL);
out:
- /*
- * As we waited the extent range, the data_rsv_map must be empty
- * in the range, as written data range will be released from it.
- * And for prealloacted extent, it will also be released when
- * its metadata is written.
- * So this is completely used as cleanup.
- */
- btrfs_qgroup_free_data(inode, alloc_start, alloc_end - alloc_start);
inode_unlock(inode);
/* Let go of our reservation. */
- btrfs_free_reserved_data_space(inode, alloc_start,
- alloc_end - alloc_start);
+ if (ret != 0)
+ btrfs_free_reserved_data_space(inode, alloc_start,
+ alloc_end - cur_offset);
return ret;
}