On 2019/2/13 上午12:03, David Sterba wrote:
> On Thu, Jan 24, 2019 at 09:31:43AM -0500, Josef Bacik wrote:
>> Previously callers to btrfs_end_transaction_throttle() would commit the
>> transaction if there wasn't enough delayed refs space. This happens in
>> relocation, and if the fs is relatively empty we'll run out of delayed
>> refs space basically immediately, so we'll just be stuck in this loop of
>> committing the transaction over and over again.
>>
>> This code existed because we didn't have a good feedback mechanism for
>> running delayed refs, but with the delayed refs rsv we do now. Delete
>> this throttling code and let the btrfs_start_transaction() in relocation
>> deal with putting pressure on the delayed refs infrastructure. With
>> this patch we no longer take 5 minutes to balance a metadata only fs.
>>
>> Signed-off-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
>
> For the record, this has been merged to 5.0-rc5
>
Bisecting leads me to this patch for strange balance ENOSPC.
Can be reproduced by btrfs/156, or the following small script:
------
#!/bin/bash
dev="/dev/test/test"
mnt="/mnt/btrfs"
_fail()
{
echo "!!! FAILED: $@ !!!"
exit 1
}
do_work()
{
umount $dev &> /dev/null
umount $mnt &> /dev/null
mkfs.btrfs -b 1G -m single -d single $dev -f > /dev/null
mount $dev $mnt
for i in $(seq -w 0 511); do
# xfs_io -f -c "falloc 0 1m" $mnt/file_$i > /dev/null
xfs_io -f -c "pwrite 0 1m" $mnt/inline_$i > /dev/null
done
sync
btrfs balance start --full $mnt || return 1
sync
btrfs balance start --full $mnt || return 1
umount $mnt
}
failed=0
for i in $(seq -w 0 24); do
echo "=== run $i ==="
do_work
if [ $? -eq 1 ]; then
failed=$(($failed + 1))
fi
done
if [ $failed -ne 0 ]; then
echo "!!! failed $failed/25 !!!"
else
echo "=== all passes ==="
fi
------
For v4.20, it will fail at the rate around 0/25 ~ 2/25 (very rare).
But at that patch (upstream commit
302167c50b32e7fccc98994a91d40ddbbab04e52), the failure rate raise to 25/25.
Any idea for that ENOSPC problem?
As it looks really wired for the 2nd full balance to fail even we have
enough unallocated space.
Thanks,
Qu
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