On Tue, Dec 01, 2015 at 03:32:49PM +0100, Michal Hocko wrote:
> From: Michal Hocko <mho...@suse.com>
>
> b92b1b89a33c ("virtio: force vring descriptors to be allocated from
> lowmem") tried to exclude highmem pages for descriptors so it cleared
> __GFP_HIGHMEM from a given gfp mask. The patch also cleared __GFP_HIGH
> which doesn't make much sense for this fix because __GFP_HIGH only
> controls access to memory reserves and it doesn't have any influence
> on the zone selection. Some of the call paths use GFP_ATOMIC and
> dropping __GFP_HIGH will reduce their changes for success because the
> lack of access to memory reserves.
>
> Signed-off-by: Michal Hocko <mho...@suse.com>
> ---
> Hi,
> I have stumbled over this code while looking at other issue [1]. I think
> that using __GFP_HIGH simply got there because of its confusing name. It
> doesn't have anything to do with the highmem zone.
>
> The patch is based on the current linux-next.
>
> I think that clearing __GFP_HIGHMEM is bogus in the current code because
> all code paths either use GFP_KERNEL or GFP_ATOMIC and those do not fall
> back to the highmem zone but I have kept it because clearing the flag
> cannot be harmful.
>
> [1] http://lkml.kernel.org/r/87h9k4kzcv.fsf%40yhuang-dev.intel.com
>
> drivers/virtio/virtio_ring.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
Thanks for cleaning this up:
Acked-by: Will Deacon <will.dea...@arm.com>
Will
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 14e7ce9b3e96..734de927c89d 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -110,7 +110,7 @@ static struct vring_desc *alloc_indirect(struct virtqueue
> *_vq,
> * otherwise virt_to_phys will give us bogus addresses in the
> * virtqueue.
> */
> - gfp &= ~(__GFP_HIGHMEM | __GFP_HIGH);
> + gfp &= ~__GFP_HIGHMEM;
>
> desc = kmalloc(total_sg * sizeof(struct vring_desc), gfp);
> if (!desc)
> --
> 2.6.2
>
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