Re: [PATCH 8/9] btrfs: wait for delayed iputs on no space

[Chris Mason <clm@fb.com>]

On 04/09/2015 12:34 AM, Zhaolei wrote:
> From: Zhao Lei <zhaolei@cn.fujitsu.com>
> 
> btrfs will report no_space when we run following write and delete
> file loop:
>  # FILE_SIZE_M=[ 75% of fs space ]
>  # DEV=[ some dev ]
>  # MNT=[ some dir ]
>  #
>  # mkfs.btrfs -f "$DEV"
>  # mount -o nodatacow "$DEV" "$MNT"
>  # for ((i = 0; i < 100; i++)); do dd if=/dev/zero of="$MNT"/file0 bs=1M count="$FILE_SIZE_M"; rm -f "$MNT"/file0; done
>  #
> 
> Reason:
>  iput() and evict() is run after write pages to block device, if
>  write pages work is not finished before next write, the "rm"ed space
>  is not freed, and caused above bug.
> 
> Fix:
>  We can add "-o flushoncommit" mount option to avoid above bug, but
>  it have performance problem. Actually, we can to wait for on-the-fly
>  writes only when no-space happened, it is which this patch do.

Can you please change this so we only do this flush if the first commit
doesn't free up enough space?  I think this is going to have a
performance impact as the FS fills up.

-chris