On 05/07/2011 05:29 PM, slyich@xxxxxxxxx wrote:
Observed as a large delay when --mixed filesystem is filled up.
Test example:
1. create tiny --mixed FS:
$ dd if=/dev/zero of=2G.img seek=$((2048 * 1024 * 1024 - 1)) count=1 bs=1
$ mkfs.btrfs --mixed 2G.img
$ mount -oloop 2G.img /mnt/ut/
2. Try to fill it up:
$ dd if=/dev/urandom of=10M.file bs=10240 count=1024
$ seq 1 256 | while read file_no; do echo $file_no; time cp 10M.file ${file_no}.copy; done
Up to '200.copy' it goes fast, but when disk fills-up each -ENOSPC
message takes 3 seconds to pop-up _every_ ENOSPC (and in usermode linux
it's even more: 30-60 seconds!). (Maybe, time depends on kernel's timer resolution).
No IO, no CPU load, just rescheduling. Some debugging revealed busy spinning
in shrink_delalloc.
Signed-off-by: Sergei Trofimovich<slyfox@xxxxxxxxxx>
---
fs/btrfs/extent-tree.c | 4 ++++
1 files changed, 4 insertions(+), 0 deletions(-)
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 9ee6bd5..9f5fdd3 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -3425,6 +3425,10 @@ static int shrink_delalloc(struct btrfs_trans_handle *trans,
if (reserved == 0)
return 0;
+ /* nothing to shrink - nothing to reclaim */
+ if (root->fs_info->delalloc_bytes == 0)
+ return 0;
+
max_reclaim = min(reserved, to_reclaim);
while (loops< 1024) {
Nice catch, you can add
Reviewed-by: Josef Bacik <josef@xxxxxxxxxx>
Thanks,
Josef
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