Re: Cleancache support in XFS

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Thu, Nov 21, 2013 at 10:07:41AM -0600, Ben Myers wrote:
> Hi James,
> 
> On Thu, Nov 21, 2013 at 01:35:59PM +0000, James Dingwall wrote:
> > Dave Chinner wrote:
> > >On Tue, Jul 23, 2013 at 08:23:00AM +0100, James Dingwall wrote:
> > >>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?
> > >I think that's sufficient. Send it to the list ;)
> > >
> > >Cheers,
> > >
> > >Dave.
> > I had a quick look through the 3.12 sources today and noted that
> > this patch did not seem to get picked up.  I'm still running with it
> > and am now on 3.12 with no observed problems.  I'm happy to rebase
> > against 3.12 if required but it seems simple enough it should go on
> > cleanly to the current development tree.
> 
> It hasn't been picked up because I'm not quite convinced it's ok to do this.

In terms of process (acks, etc) or how it functions/meshes with cleancache?

> See if you can get a Dave, Christoph, or Eric to offer a Reviewed-by with a
> little explanation of why this is ok and I'll pull it in.  ;)

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