On Thu, Nov 01, 2018 at 03:40:35PM -0700, Daniel Verkamp wrote:
> From: Changpeng Liu <changpeng.liu@intel.com>
> 
> In commit 88c85538, "virtio-blk: add discard and write zeroes features
> to specification" (https://github.com/oasis-tcs/virtio-spec), the virtio
> block specification has been extended to add VIRTIO_BLK_T_DISCARD and
> VIRTIO_BLK_T_WRITE_ZEROES commands.  This patch enables support for
> discard and write zeroes in the virtio-blk driver when the device
> advertises the corresponding features, VIRTIO_BLK_F_DISCARD and
> VIRTIO_BLK_F_WRITE_ZEROES.
> 
> Signed-off-by: Changpeng Liu <changpeng.liu@intel.com>
> Signed-off-by: Daniel Verkamp <dverkamp@chromium.org>
> ---
> dverkamp: I've picked up this patch and made a few minor changes (as
> listed below); most notably, I changed the kmalloc back to GFP_ATOMIC,
> since it can be called from a context where sleeping is not allowed.
> To prevent large allocations, I've also clamped the maximum number of
> discard segments to 256; this results in a 4K allocation and should be
> plenty of descriptors for most use cases.
> 
> I also removed most of the description from the commit message, since it
> was duplicating the comments from virtio_blk.h and quoting parts of the
> spec without adding any extra information.  I have tested this iteration
> of the patch using crosvm with modifications to enable the new features:
> https://chromium.googlesource.com/chromiumos/platform/crosvm/
> 
> v9 fixes a number of review issues; I didn't attempt to optimize the
> single-element write zeroes case, so it still does an allocation per
> request (I did not see any easy place to put the payload that would
> avoid the allocation).
> 
> CHANGELOG:
> v9: [dverkamp] fix LE types in discard struct; cleanups from Ming Lei
> v8: [dverkamp] replace shifts by 9 with SECTOR_SHIFT constant
> v7: [dverkamp] use GFP_ATOMIC for allocation that may not sleep; clarify
> descriptor flags field; comment wording cleanups.
> v6: don't set T_OUT bit to discard and write zeroes commands.
> v5: use new block layer API: blk_queue_flag_set.
> v4: several optimizations based on MST's comments, remove bit field
> usage for command descriptor.
> v3: define the virtio-blk protocol to add discard and write zeroes
> support, first version implementation based on proposed specification.
> v2: add write zeroes command support.
> v1: initial proposal implementation for discard command.
> ---
>  drivers/block/virtio_blk.c      | 83 ++++++++++++++++++++++++++++++++-
>  include/uapi/linux/virtio_blk.h | 54 +++++++++++++++++++++
>  2 files changed, 135 insertions(+), 2 deletions(-)

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>