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Re: Cleancache support in XFS

To: James Dingwall <james.dingwall@xxxxxxxxxxx>
Subject: Re: Cleancache support in XFS
From: Ben Myers <bpm@xxxxxxx>
Date: Thu, 21 Nov 2013 10:07:41 -0600
Cc: Dave Chinner <david@xxxxxxxxxxxxx>, xfs@xxxxxxxxxxx, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <528E0C3F.3010401@xxxxxxxxxxx>
References: <20130501223022.GQ10481@dastard> <518222D3.3080109@xxxxxxxxxxx> <20130522192834.GD10617@xxxxxxxxxxxxxxxxxxx> <519F1708.10603@xxxxxxxxxxx> <20130607170826.GA6925@xxxxxxxxxxxxxxxxxxx> <51E8E834.6080509@xxxxxxxxxxx> <20130722154812.GC30300@xxxxxxxxxxxxxxxxxxx> <51EE2F54.80701@xxxxxxxxxxx> <20130723082700.GK19986@dastard> <528E0C3F.3010401@xxxxxxxxxxx>
User-agent: Mutt/1.5.20 (2009-06-14)
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.
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.  ;)

Thanks,
        Ben

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