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| Started by | Michal Hocko <mhocko@kernel.org> |
|---|---|
| First post | 2015-12-01 15:40 +0100 |
| Last post | 2015-12-07 12:30 +0100 |
| Articles | 3 — 3 participants |
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[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
| From | Michal Hocko <mhocko@kernel.org> |
|---|---|
| Date | 2015-12-01 15:40 +0100 |
| Subject | [PATCH] virtio: Do not drop __GFP_HIGH in alloc_indirect |
| Message-ID | <qAUg2-2ob-5@gated-at.bofh.it> |
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
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| From | Will Deacon <will.deacon@arm.com> |
|---|---|
| Date | 2015-12-01 17:20 +0100 |
| Message-ID | <qAVOO-3v2-23@gated-at.bofh.it> |
| In reply to | #1280909 |
On Tue, Dec 01, 2015 at 03:32:49PM +0100, Michal Hocko wrote:
> 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(-)
Thanks for cleaning this up:
Acked-by: Will Deacon <will.deacon@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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| From | Mel Gorman <mgorman@techsingularity.net> |
|---|---|
| Date | 2015-12-07 12:30 +0100 |
| Message-ID | <qD29s-3NM-17@gated-at.bofh.it> |
| In reply to | #1280909 |
On Tue, Dec 01, 2015 at 03:32:49PM +0100, Michal Hocko wrote:
> 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>
Reviewed-by: Mel Gorman <mgorman@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
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