Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1280909

[PATCH] virtio: Do not drop __GFP_HIGH in alloc_indirect

Show all headers | View raw

From: Michal Hocko <mhocko@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@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

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Back to linux.kernel | Previous | Next — Next in thread | Find similar | Unroll thread

Thread

[PATCH] virtio: Do not drop __GFP_HIGH in alloc_indirect Michal Hocko <mhocko@kernel.org> - 2015-12-01 15:40 +0100
  Re: [PATCH] virtio: Do not drop __GFP_HIGH in alloc_indirect Will Deacon <will.deacon@arm.com> - 2015-12-01 17:20 +0100
  Re: [PATCH] virtio: Do not drop __GFP_HIGH in alloc_indirect Mel Gorman <mgorman@techsingularity.net> - 2015-12-07 12:30 +0100

csiph-web