* [PATCH] virtio: Do not drop __GFP_HIGH in alloc_indirect
@ 2015-12-01 14:32 Michal Hocko
2015-12-01 16:17 ` Will Deacon
` (2 more replies)
0 siblings, 3 replies; 6+ messages in thread
From: Michal Hocko @ 2015-12-01 14:32 UTC (permalink / raw)
To: Michael S. Tsirkin; +Cc: Will Deacon, virtualization, LKML, Michal Hocko
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
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH] virtio: Do not drop __GFP_HIGH in alloc_indirect
2015-12-01 14:32 [PATCH] virtio: Do not drop __GFP_HIGH in alloc_indirect Michal Hocko
@ 2015-12-01 16:17 ` Will Deacon
2015-12-07 11:29 ` Mel Gorman
2015-12-07 11:29 ` Mel Gorman
2 siblings, 0 replies; 6+ messages in thread
From: Will Deacon @ 2015-12-01 16:17 UTC (permalink / raw)
To: Michal Hocko; +Cc: Michael S. Tsirkin, virtualization, LKML, Michal Hocko
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
>
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] virtio: Do not drop __GFP_HIGH in alloc_indirect
@ 2015-12-01 16:17 ` Will Deacon
0 siblings, 0 replies; 6+ messages in thread
From: Will Deacon @ 2015-12-01 16:17 UTC (permalink / raw)
To: Michal Hocko; +Cc: virtualization, Michal Hocko, LKML, Michael S. Tsirkin
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
>
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] virtio: Do not drop __GFP_HIGH in alloc_indirect
2015-12-01 14:32 [PATCH] virtio: Do not drop __GFP_HIGH in alloc_indirect Michal Hocko
2015-12-01 16:17 ` Will Deacon
@ 2015-12-07 11:29 ` Mel Gorman
2015-12-07 11:29 ` Mel Gorman
2 siblings, 0 replies; 6+ messages in thread
From: Mel Gorman @ 2015-12-07 11:29 UTC (permalink / raw)
To: Michal Hocko
Cc: Michael S. Tsirkin, Will Deacon, Huang, Ying, virtualization,
LKML, Michal Hocko
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
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] virtio: Do not drop __GFP_HIGH in alloc_indirect
2015-12-01 14:32 [PATCH] virtio: Do not drop __GFP_HIGH in alloc_indirect Michal Hocko
2015-12-01 16:17 ` Will Deacon
2015-12-07 11:29 ` Mel Gorman
@ 2015-12-07 11:29 ` Mel Gorman
2 siblings, 0 replies; 6+ messages in thread
From: Mel Gorman @ 2015-12-07 11:29 UTC (permalink / raw)
To: Michal Hocko
Cc: Michal Hocko, Michael S. Tsirkin, Huang, Ying, Will Deacon, LKML,
virtualization
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
^ permalink raw reply [flat|nested] 6+ messages in thread
* [PATCH] virtio: Do not drop __GFP_HIGH in alloc_indirect
@ 2015-12-01 14:32 Michal Hocko
0 siblings, 0 replies; 6+ messages in thread
From: Michal Hocko @ 2015-12-01 14:32 UTC (permalink / raw)
To: Michael S. Tsirkin; +Cc: Michal Hocko, Will Deacon, LKML, virtualization
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
^ permalink raw reply related [flat|nested] 6+ messages in thread
end of thread, other threads:[~2015-12-07 11:29 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
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2015-12-01 14:32 [PATCH] virtio: Do not drop __GFP_HIGH in alloc_indirect Michal Hocko
2015-12-01 16:17 ` Will Deacon
2015-12-01 16:17 ` Will Deacon
2015-12-07 11:29 ` Mel Gorman
2015-12-07 11:29 ` Mel Gorman
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2015-12-01 14:32 Michal Hocko
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