On Tue, 19 Aug 2014 10:58:09 -0400, Chris Mason wrote:
> On 08/19/2014 10:23 AM, David Sterba wrote:
>> On Tue, Aug 19, 2014 at 07:58:20PM +0800, Fengguang Wu wrote:
>>> We noticed an xfstests failure on commit
>>>
>>> 8d875f95da43c6a8f18f77869f2ef26e9594fecc ("btrfs: disable strict file
>>> flushes for renames and truncates")
>>>
>>> It's 100% reproducible in the 5 test runs.
>>
>> Same here, different mkfs configurations.
>>
>> generic/226 28s ... [16:11:52] [16:12:55] - output mismatch (see
>> /root/xfstests/results//generic/226.out.bad)
>> --- tests/generic/226.out 2013-05-29 17:16:03.000000000 +0200
>> +++ /root/xfstests/results//generic/226.out.bad 2014-08-19
>> 16:12:55.000000000 +0200
>> @@ -1,6 +1,8 @@
>> QA output created by 226
>> --> mkfs 256m filesystem
>> --> 16 buffered 64m writes in a loop
>> -1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
>> +1 2 3 4 pwrite64: No space left on device
>> +5 6 7 8 9 10 11 12 pwrite64: No space left on device
>> +13 14 15 16
>>
>> enospc on a small filesystem (256M)
>
> I'm calling filemap flush more often, but otherwise everything else is
> the same. I'll take a look.
The above patch also introduced a performance regression(~70%DOWN).
We can reproduce this regression by fio, here is the config:
[global]
ioengine=falloc
iodepth=1
direct=0
buffered=0
directory=<mnt>
nrfiles=1
filesize=100m
group_reporting
[sequential aio-dio write]
stonewall
ioengine=posixaio
numjobs=1
iodepth=128
buffered=0
direct=0
rw=write
bs=64k
filename=fragmented_file
I found the problem is caused by the following function:
int btrfs_release_file(struct inode *inode, struct file *filp)
{
...
filemap_flush(inode->i_mapping);
return 0;
}
I don't think we need flush file at most situation. Ext4 flushes the file only
after someone truncate the file to be zero-length, I don't know the real reason
why ext4 flush the file only after the file is truncated, someone said it is to
reduce the risk that the users find a zero-length file after a crash, which
happens
after truncate-write-close process.
If we change btrfs_release_file by ext4's implementation, both the failure of
xfstests's generic/226 and performance regression can be fixed.
Thanks
Miao
>
> -chris
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majord...@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at http://www.tux.org/lkml/
>
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
