Re: [Xen-devel][PATCH]: Support dynamic resizing of vbds

["J. Roeleveld" <joost@xxxxxxxxxxxx>]

On Tuesday 16 March 2010 22:24:02 J. Roeleveld wrote:
> On Tuesday 16 March 2010 03:50:18 Ky Srinivasan wrote:
> > >>> On 3/14/2010 at  9:49 AM, in message
> >
> > <f4527be1003140649p6d9cced6u7d1fde07897ae70c@xxxxxxxxxxxxxx>, Andrew Lyon
> >
> > <andrew.lyon@xxxxxxxxx> wrote:
> > > On Fri, Mar 12, 2010 at 10:41 AM, J. Roeleveld <joost@xxxxxxxxxxxx> 
wrote:
> > >> On Tuesday 09 March 2010 20:56:11 Ky Srinivasan wrote:
> > >>> The attached patch supports dynamic resizing of vbds.
> > >>>
> > >>> Signed-off-by: K. Y. Srinivasan <ksrinivasan@xxxxxxxxxx>
> > >>
> > >> Thank you for this.
> > >>
> > >> The patch applied succesfully against the gentoo-xen kernel
> > >> (2.6.29-xen-r4)
> > >>
> > >> I will test the patch on my system during the next week and provide
> > >
> > > feedback.
> >
> > Thanks. Looking forward to your feedback.
> >
> > K. Y
> 
> Ok, finally got time to test it.
> Not seen any major crashes, but my domU and filesystem did end up in an
> unusable state.
> 
> I also noticed that the change-entries in the logs didn't show up until I
> "touched" the drive.
> Eg: "ls <mount point>"
> 
> When trying to do an online resize, "resize2fs" refused, saying the
>  filesystem was already using the full space:
> --
> storage ~ # resize2fs /dev/sdb1
> resize2fs 1.41.9 (22-Aug-2009)
> The filesystem is already 104857600 blocks long.  Nothing to do!
> --
> 
> This was then 'resolved' by umount/mount of the filesystem:
> --
> storage ~ # umount /data/homes/
> storage ~ # mount /data/homes/
> storage ~ # resize2fs /dev/sdb1
> resize2fs 1.41.9 (22-Aug-2009)
> Filesystem at /dev/sdb1 is mounted on /data/homes; on-line resizing
>  required old desc_blocks = 25, new_desc_blocks = 29
> Performing an on-line resize of /dev/sdb1 to 117964800 (4k) blocks.
> --
> 
> These actions were take in the domU.
> 
> The patch informs the domU about the new size, but the new size is not
> cascaded to all the levels.
> 
> I'm not familiar enough with the kernel internals to point to where the
> missing part is.
> 
> My ideal situation would allow the folliowing to work without additional
> steps:
> 
> dom0: lvresize -L+10G /dev/vg/foo
> domU: resizefs /dev/sdb1
> 
> (with "/dev/vg/foo" exported to domU as "/dev/sdb1")
> 
> Right now, I need to do the following:
> dom0: lvresize -L+10G /dev/vg/foo
> domU: ls /mnt/sdb1
> domU: umount /mnt/sdb1
> domU: mount /mnt/sdb1
> domU: resizefs /dev/sdb1
> 
> During the 2nd attempt, when trying to umount the filesystem after
>  increasing it again leads to the domU having a 100% I/O wait.
> The logs themselves do not, however, show any usefull information.
> 
> I waited for about 30 minutes and saw no change to this situation.
> 
> I am afraid that for now I will revert back to not having this patch
>  applied and use the 'current' method of increasing the filesystem sizes.
> 
> Please let me know if there is any further testing I can help with.
> 
> --
> Joost Roeleveld
> 

Update,

After killing the domU, I saw the following in my dom0:

--
VBD Resize: new size 943718400
VBD Resize: new size 1048576000
INFO: task blkback.3.sdb1:21647 blocked for more than 480 seconds.
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
blkback.3.sdb D 0000000000000002     0 21647      2
 ffff88002b54f550 0000000000000246 ffff88002ef08000 0000000600000000
 ffff88002f9bf800 ffffffff806952c0 ffffffff806952c0 ffff88002eeee550
 ffff88002b54f778 000000002eee6800 0000000000000000 ffff88002b54f778
Call Trace:
 [<ffffffff804d6ece>] printk+0x4e/0x58
 [<ffffffff804d9387>] __down_read+0x101/0x119
 [<ffffffff803d301e>] xenbus_transaction_start+0x15/0x62
 [<ffffffff803d8843>] vbd_resize+0x50/0x120
 [<ffffffff803d747c>] blkif_schedule+0x7e/0x4ae
 [<ffffffff803d73fe>] blkif_schedule+0x0/0x4ae
 [<ffffffff8023f8de>] kthread+0x47/0x73
 [<ffffffff8020b2ea>] child_rip+0xa/0x20
 [<ffffffff8023f897>] kthread+0x0/0x73
 [<ffffffff8020b2e0>] child_rip+0x0/0x20
--

(this was the result from "dmesg"

The ID of the domU was "3" and the device of the filesystem in the domU is 
"sdb1"
Eg. this matches the above error-message.

--
Joost

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