linux-ext4 - Re: ceph and ext4

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Date:	Sun, 12 Feb 2012 11:50:23 -0800
From:	Yehuda Sadeh Weinraub <yehuda.sadeh@...amhost.com>
To:	Andreas Dilger <adilger@...mcloud.com>
Cc:	chb@....de,
	"ceph-devel@...r.kernel.org" <ceph-devel@...r.kernel.org>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
	Jian Yu <yujian@...mcloud.com>
Subject: Re: ceph and ext4

On Sun, Feb 12, 2012 at 9:18 AM, Andreas Dilger <adilger@...mcloud.com> wrote:
> On 2012-02-11, at 9:05 PM, Yehuda Sadeh Weinraub wrote:
>> On Fri, Dec 9, 2011 at 2:24 PM, Andreas Dilger <adilger@...mcloud.com> wrote:
>>>
>>> On 2011-12-08, at 3:59 PM, Christian Brunner wrote:
>>>> 2011/11/15 Andreas Dilger <adilger@...mcloud.com>:
>>>>> Coincidentally, we have someone working in those patches again. The main obstacle for accepting the previous patch as-is was that Ted wanted to add support for "medium-sized" xattrs that are addressed as a string of blocks, instead of via an inode.
>>>>
>>>> Did you make progress with this. I'm still having serious trouble with
>>>> btrfs and would like to try these.
>>>
>>> The latest patches are available at http://review.whamcloud.com/1708, but are based on the RHEL6.1 2.6.32 kernel.  The work to implement "medium-sized" xattrs was more complex than anticipated, and is not finished yet.
>>>
>>> The use of external inode xattrs is working, which allows xattr sizes up to 64kB.  The 64kB limit is imposed by the VFS and could potentially be increased.
>>
>> I was able to get those compile on a recent kernel.
>
> It would be useful if you could send me the updated patch, if there were
> any significant changes.

I pushed it to the the ext4-large-xattr branch, here:

https://github.com/NewDreamNetwork/ceph-client.git

>
>> One issue that I
>> see is that it will only use a separate inode for the xattr if the
>> xattr is big enough. However, it may be that we ran out of enough
>> space to set a smaller xattr, and in that case we would fail setting
>> it even though we'd be able to set a larger xattr.
>> Another related issue, is that the number of xattrs that can be used
>> is still limited (by what can be indexed in a single block?).
>
> That is true with the current patch.  When the "medium sized" xattrs are
> finished, then there will be 64kB of space for xattrs in the external
> block(s), which could be both xattr headers and data.

Is there any progress with this feature? Is there any public
repository where we can take a look at that?

Thanks,
Yehuda
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