Michal Hocko
2015-Dec-01 14:32 UTC
[PATCH] virtio: Do not drop __GFP_HIGH in alloc_indirect
From: Michal Hocko <mhocko at 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 <mhocko at 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(-)
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
Will Deacon
2015-Dec-01 16:17 UTC
[PATCH] virtio: Do not drop __GFP_HIGH in alloc_indirect
On Tue, Dec 01, 2015 at 03:32:49PM +0100, Michal Hocko wrote:> From: Michal Hocko <mhocko at 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 <mhocko at 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.deacon at 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 >
On Tue, Dec 01, 2015 at 03:32:49PM +0100, Michal Hocko wrote:> From: Michal Hocko <mhocko at 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 <mhocko at suse.com>Reviewed-by: Mel Gorman <mgorman at techsingularity.net> It also has been tested by Ying Huang and found to have fixed a page allocation failure problem in 4.4-rc3 in the Intel 0-day testing infrastructure. -- Mel Gorman SUSE Labs