Cleancache support in XFS

[James Dingwall]

Konrad Rzeszutek Wilk wrote:
> On Fri, Jul 19, 2013 at 08:18:12AM +0100, James Dingwall wrote:
>> Konrad Rzeszutek Wilk wrote:
>>> On Fri, May 24, 2013 at 08:30:16AM +0100, James Dingwall wrote:
>>>> Konrad Rzeszutek Wilk wrote:
>>>>> On Thu, May 02, 2013 at 09:24:51AM +0100, James Dingwall wrote:
>>>>>> Dave Chinner wrote:
>>>>>>> On Wed, May 01, 2013 at 11:20:44AM -0500, Ben Myers wrote:
>>>>>>>> Hi James,
>>>>> Hey folks,
>>>>> I am walking through my vacation-emails-mbox.
>>>>>
>>>>>>>> On Wed, May 01, 2013 at 01:39:09PM +0100, James Dingwall wrote:
>>>>>>>>> In reference to: http://oss.sgi.com/archives/xfs/2012-05/msg00046.html
>>>>>>>>>
>>>>>>>>> $ grep -r cleancache fs/xfs
>>>>>>>>> on the 3.9 kernel source suggests that no patch was submitted to
>>>>>>>>> enable cleancache for the XFS filesystem.  Since it was suggested
>>>>>>>>> that this could be a one liner I've had a go and my first effort is
>>>>>>>>> inline below.  While this seems to compile OK I have no experience
>>>>>>>>> in filesystems so I would appreciate it if anyone can point out that
>>>>>>>>> it is obviously wrong and likely to eat my data before I try booting
>>>>>>>>> the kernel.
>>>>>>>>>
>>>>>>>>> If it seems a reasonable attempt what would be the best way to check
>>>>>>>>> that it isn't doing nasty things?
>>>>>>>> Hrm.. Looks like there is a doc in Documentation/vm/cleancache.txt which
>>>>>>>> includes a list of attributes the filesystem needs to have to work properly
>>>>>>>> with cleancache.
>>>>>>> So, those points are:
>>>>>> I had started to look at these too but I feel very out of my depth!
>>>>>> I had similar conclusions to what Dave wrote but I don't think my
>>>>>> thoughts should carry very much (any) weight.  Anyway I gambled and
>>>>>> booted my xen domU with this patch and so far so good...  xen top
>>>>>> shows that tmem is now being used where previously it wasn't.  I'll
>>>>>> try running the xfstests at the weekend after a couple more days up
>>>>>> time to see what happens.
>>>>> And how did it go?
>>>> I am running the patch I created on 3.9.3 on half of my xen guests
>>>> now and have not noticed any stability or filesystem problems.  xl
>>>> top with 'T' shows that the guests running with it are using
>>>> ephemeral pages were those without do not.  I did do some runs with
>>>> xfstests which had some failures but they were present with and
>>>> without the patch.  The best I can really offer is that it works for
>>>> me, ymmv.  The patch is available as commit
>>>> c725011c4fc5d47e12d131f61bd91a58a40036b5 in
>>>> https://github.com/JKDingwall/linux.git xfs-enable-cleancache or in
>>>> the first message of this thread.
>>> Hey James,
>>>
>>> I've run this patch on my local tree and it looks to work right. I am
>>> saying "looks" as I am hitting some other issue that I believe are
>>> unralted to the patch - but I need to figure them out before I can
>>> comfortably say: "Yes, this looks right and works for me as well."
>>>
>>> Stay tuned.
>> Just to add that I have also had no observable problems running this
>> patch on 3.10.0 or 3.10.1.
> Yup. And I tested it as well. In other words if you would like to add
> Acked-by from me that would be super. Thanks!
My patch is now available in https://github.com/JKDingwall/linux.git 
xfs-enable-cleancache as commit id 
6d50663e4ec88b7e1fd872b12ac310b1f4bb38c6.  I have rebased it on 3.10 
with KRW's Acked-by and my Signed-off-by in the commit message.  Is it 
reasonable for this to be considered for 3.12 or would further testing 
be required?

Thanks,
James