Re: [Qemu-devel] [RFC PATCH 0/5] Make discard visible to the guests

[Stefan Hajnoczi]

On Fri, Feb 08, 2013 at 02:06:10PM +0100, Paolo Bonzini wrote:
> The major missing step in order to implement thin provisioning is
> exposing discard commands to the guest.  This series implements
> minimal control of this capability.
> 
> Whether to enable discard or not is made a host parameter, so that
> choices in storage technology do not affect the hardware that the
> guest sees.  While it is still possible to fine-tune the parameters
> (at least for SCSI disks), the default granularity is set to the
> logical block size or 4k, whichever is largest, because cluster
> sizes below 4k are rarely used and 4K is a typical block size
> for files.
> 
> Nevertheless, using DISCARD with filesystems can cause very severe
> fragmentation, so it is left default-off for now.  This can change later
> when we implement the "anchor" operation for efficient management of
> preallocated files.
> 
> Paolo
> 
> 
> Paolo Bonzini (5):
>   block: implement BDRV_O_UNMAP
>   blockdev: add discard suboption to -drive
>   qemu-nbd: add --discard option
>   blockdev: enable discard by default
>   pc: add compatibility machine types for 1.4
> 
>  block.c               | 25 +++++++++++++++++++++++++
>  blockdev.c            | 11 +++++++++++
>  hw/block-common.h     |  2 +-
>  hw/ide/qdev.c         |  5 ++++-
>  hw/pc.h               | 32 ++++++++++++++++++++++++++++++++
>  hw/pc_piix.c          | 18 ++++++++++++++++--
>  hw/pc_q35.c           | 19 ++++++++++++++++---
>  hw/scsi-disk.c        | 13 ++++++++++---
>  include/block/block.h |  2 ++
>  qemu-io.c             | 11 +++++++++--
>  qemu-nbd.c            | 18 +++++++++++++++---
>  qemu-nbd.texi         |  4 ++++
>  qemu-options.hx       |  2 ++
>  13 files changed, 147 insertions(+), 15 deletions(-)
> 
> -- 
> 1.8.1.2
> 
> 

I posted one comment, otherwise looks good.