[BUG]
Btrfs will report false ENOSPC balancing metadata chunk.
The following script can easily reproduce it:
#!/bin/bash
dev=/dev/test/test
mnt=/mnt/btrfs
umount $dev &> /dev/null
umount $mnt &> /dev/null
mkfs.btrfs -f $dev
mount $dev $mnt
btrfs subv create $mnt/subv
for ((i = 0; i < 1024; i++)) do
xfs_io -f -c "pwrite 0 4k" $mnt/subv/file_$i > /dev/null
done
btrfs balance start -m $mnt
[CAUSE]
It's metadata space_info::bytes_may_use causing the problem.
For above case, we need to reserve enough metadata space for all the
created small files.
[FIX]
The most straightforward is to sync the fs before balancing metadata
chunks.
We could enhance the kernel bytes_may_use calculation, but I doubt about
the complexity.
So I take the easy fix to reduce the false ENOSPC reports.
Signed-off-by: Qu Wenruo <w...@suse.com>
---
cmds-balance.c | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)
diff --git a/cmds-balance.c b/cmds-balance.c
index 15dc385e..a617a1d2 100644
--- a/cmds-balance.c
+++ b/cmds-balance.c
@@ -24,6 +24,7 @@
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>
+#include <btrfsutil.h>
#include "kerncompat.h"
#include "ctree.h"
@@ -32,6 +33,7 @@
#include "commands.h"
#include "utils.h"
+#include "utils.h"
#include "help.h"
static const char * const balance_cmd_group_usage[] = {
@@ -455,6 +457,22 @@ static int do_balance(const char *path, struct
btrfs_ioctl_balance_args *args,
printf("\nStarting balance without any filters.\n");
}
+ /*
+ * There may be many over-reserved space for metadata block groups,
+ * especially for inlined file extents.
+ *
+ * Do a sync here will free those over-reserved space and hugely
+ * reduce the possibility of some false ENOSPC
+ */
+ if (args->flags & BTRFS_BALANCE_METADATA) {
+ ret = btrfs_util_sync(path);
+ if (ret) {
+ error("failed to sync the fs before balance: %m");
+ ret = -errno;
+ goto out;
+ }
+ }
+
ret = ioctl(fd, BTRFS_IOC_BALANCE_V2, args);
if (ret < 0) {
/*
--
2.18.0
