[Ocfs2-devel] [PATCH 0/8] ocfs2: fix ocfs2 direct io code patch to support sparse file and data ordering semantics

[Joseph Qi]

Hi Ryan,

On 2015/10/8 11:12, Ryan Ding wrote:
> Hi Joseph,
> 
> On 09/28/2015 06:20 PM, Joseph Qi wrote:
>> Hi Ryan,
>> I have gone through this patch set and done a simple performance test
>> using direct dd, it indeed brings much performance promotion.
>>           Before      After
>> bs=4K    1.4 MB/s    5.0 MB/s
>> bs=256k  40.5 MB/s   56.3 MB/s
>>
>> My questions are:
>> 1) You solution is still using orphan dir to keep inode and allocation
>> consistency, am I right? From our test, it is the most complicated part
>> and has many race cases to be taken consideration. So I wonder if this
>> can be restructured.
> I have not got a better idea to do this. I think the only reason why direct io using orphan is to prevent space lost when system crash during append direct write. But maybe a 'fsck -f' will do that job. Is it necessary to use orphan?
The idea is taken from ext4, but since ocfs2 is cluster filesystem, so
it is much more complicated than ext4.
And fsck can only be used offline, but using orphan is to perform
recovering online. So I don't think fsck can replace it in all cases.

>> 2) Rather than using normal block direct io, you introduce a way to use
>> write begin/end in buffer io. IMO, if it wants to perform like direct
>> io, it should be committed to disk by forcing committing journal. But
>> journal committing will consume much time. Why does it bring performance
>> promotion instead?
> I use buffer io to write only the zero pages. Actual data payload is written as direct io. I think there is no need to do a force commit. Because direct means "Try to minimize cache effects of the I/O to and from this file.", it does not means "write all data & meta data to disk before write return".
So this is protected by "UNWRITTEN" flag, right?

>> 3) Do you have a test in case of lack of memory?
> I tested it in a system with 2GB memory. Is that enough?
What I mean is doing many direct io jobs in case system free memory is
low.

Thanks,
Joesph

> 
> Thanks,
> Ryan
>>
>> On 2015/9/11 16:19, Ryan Ding wrote:
>>> The idea is to use buffer io(more precisely use the interface
>>> ocfs2_write_begin_nolock & ocfs2_write_end_nolock) to do the zero work beyond
>>> block size. And clear UNWRITTEN flag until direct io data has been written to
>>> disk, which can prevent data corruption when system crashed during direct write.
>>>
>>> And we will also archive a better performance:
>>> eg. dd direct write new file with block size 4KB:
>>> before this patch:
>>> 2.5 MB/s
>>> after this patch:
>>> 66.4 MB/s
>>>
>>> ----------------------------------------------------------------
>>> Ryan Ding (8):
>>>        ocfs2: add ocfs2_write_type_t type to identify the caller of write
>>>        ocfs2: use c_new to indicate newly allocated extents
>>>        ocfs2: test target page before change it
>>>        ocfs2: do not change i_size in write_end for direct io
>>>        ocfs2: return the physical address in ocfs2_write_cluster
>>>        ocfs2: record UNWRITTEN extents when populate write desc
>>>        ocfs2: fix sparse file & data ordering issue in direct io.
>>>        ocfs2: code clean up for direct io
>>>
>>>   fs/ocfs2/aops.c        | 1118 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++------------------------------------------------------------------------------------------
>>>   fs/ocfs2/aops.h        |   11 +-
>>>   fs/ocfs2/file.c        |  138 +---------------------
>>>   fs/ocfs2/inode.c       |    3 +
>>>   fs/ocfs2/inode.h       |    3 +
>>>   fs/ocfs2/mmap.c        |    4 +-
>>>   fs/ocfs2/ocfs2_trace.h |   16 +--
>>>   fs/ocfs2/super.c       |    1 +
>>>   8 files changed, 568 insertions(+), 726 deletions(-)
>>>
>>> .
>>>
>>
> 
> 
> .
>