@@ -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 +457,26 @@ 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_fd(fd);
+ if (ret) {
+ /*
+ * Failed to sync fs is a big problem, normally caused
+ * by aborted transaction.
+ */
+ error("failed to sync the fs before balance: %m");
+ ret = -errno;
+ goto out;
+ }
+ }
+
ret = ioctl(fd, BTRFS_IOC_BALANCE_V2, args);
if (ret < 0) {
/*
[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 <wqu@suse.com> --- changelog: v2: - Use btrfs_util_sync_fd() to sync the fs - Add comment on why we should error out for sync failure --- cmds-balance.c | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+)