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Re: [dm-devel] [PATCH 1/2] block: fix leaks associated with discard request payload



On Wed, 30 Jun 2010 20:55:09 +0900
FUJITA Tomonori <fujita tomonori lab ntt co jp> wrote:

> On Mon, 28 Jun 2010 17:25:36 +0200
> Christoph Hellwig <hch lst de> wrote:
> 
> > On Mon, Jun 28, 2010 at 05:14:28PM +0900, FUJITA Tomonori wrote:
> > > > While I see the problems with leaking ressources in that case I still
> > > > can't quite explain the hang I see.
> > > 
> > > Any way to reproduce the hang without ssd drives?
> > 
> > Actually the SSDs don't fully hang, they just causes lots of I/O errors
> > and hit the error handler hard.  The hard hang is when running under
> > qemu.  Apply the patch below, then create an if=scsi drive that resides
> > on an XFS filesystem, and you'll have scsi TP support in the guest:
> 
> Ok, I figured out what's wrong.
> 
> As I suspected, it's due to the partial completion.
> 
> qemu scsi driver tells that the WRITE_SAME command was successful but
> somehow the command has resid. So we retry it again and again (and
> leak some memory).
> 
> I don't know yet why qemu scsi driver is broken. Maybe there is a bug
> in it or converting discard to FS sends broken commands to the driver.

looks like your qemu WRITE_SAME patch isn't completed :)

You implement WRITE_SAME as if it doesn't do any data transfer. So
qemu scsi driver gets resid.

The reason why WRITE_SAME works now is that scsi-ml doesn't care about
resid with PC commands but it cares with FS commands.

I confirmed that qemu scsi driver gets the identical command with both
PC and FS commands and qemu calls xfsctl.


> I've put a patch to complete discard command in the all-or-nothing
> manner:
> 
> git://git.kernel.org/pub/scm/linux/kernel/git/tomo/linux-2.6-misc.git discard

Seems that I finished discard FS conversion. I'll update it on the top
of James' uprep patchset soon.


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