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Date: Tue, 6 Nov 2012 16:39:18 +0800
From: Zheng Liu <gnehzuil.liu@gmail.com>
To: Zhi Yong Wu <zwu.kernel@gmail.com>
Cc: linux-fsdevel@vger.kernel.org, linuxram@linux.vnet.ibm.com,
        Dave Chinner <david@fromorbit.com>, cmm@us.ibm.com,
        Ben Chociej <bchociej@gmail.com>,
        James Northrup <northrup.james@gmail.com>,
        linux-kernel mlist <linux-kernel@vger.kernel.org>
Subject: Re: VFS hot tracking: How to calculate data temperature?
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On Mon, Nov 05, 2012 at 10:29:39AM +0800, Zhi Yong Wu wrote:
> On Fri, Nov 2, 2012 at 4:41 PM, Zheng Liu <gnehzuil.liu@gmail.com> wrote:
> > On Fri, Nov 02, 2012 at 02:38:29PM +0800, Zhi Yong Wu wrote:
> >> Here also has another question.
> >>
> >> How to save the file temperature among the umount to be able to
> >> preserve the file tempreture after reboot?
> >>
> >> This above is the requirement from DB product.
> >> I thought that we can save file temperature in its inode struct, that
> >> is, add one new field in struct inode, then this info will be written
> >> to disk with inode.
> >>
> >> Any comments or ideas are appreciated, thanks.
> >
> > Hi Zhiyong,
> >
> > I think that we might define a callback function.  If a filesystem wants
> > to save these data, it can implement a function to save them.  The
> > filesystem can decide whether adding it or not by themselves.
> Great idea,  temperature saving function is maybe very specific to FS.
> But i am wondering if we can find one generic way to save temperature
> info at first.

I don't think a generic way is better because it cannot support a
variety of filesystems.  So maybe you must answer this question firstly:
how many filesystems do you want to save this info? such as ext4, xfs,
btrfs, etc.  Then we can try to find a generic way.  If only these three
filesystems you want to support, maybe saving in xattr is an optional
way.

Regards,
Zheng