diff mbox

[RFC,2/4] ARM: dma-mapping: IOMMU allocates pages from pool with GFP_ATOMIC

Message ID 20120822.163648.3800987367886904.hdoyu@nvidia.com
State New
Headers show

Commit Message

Hiroshi Doyu Aug. 22, 2012, 1:36 p.m. UTC 
Hi,

KyongHo Cho <pullip.cho@samsung.com> wrote @ Wed, 22 Aug 2012 14:47:00 +0200:

> vzalloc() call in __iommu_alloc_buffer() also causes BUG() in atomic context.

Right.

I've been thinking that kzalloc() may be enough here, since
vzalloc() was introduced to avoid allocation failure for big chunk of
memory, but I think that it's unlikely that the number of page array
can be so big. So I propose to drop vzalloc() here, and just simply to
use kzalloc only as below(*1).

For example, 

1920(H) x 1080(W) x 4(bytes) ~= 8MiB

For 8 MiB buffer,
  8(MiB) * 1024 = 8192(KiB)
  8192(KiB) / 4(KiB/page) = 2048 pages
  sizeof(struct page *) = 4 bytes
  2048(pages) * 4(bytes/page) = 8192(bytes) = 8(KiB)
  8(KiB) / 4(KiB/page) = 2 pages

If the above estimation is right(I hope;)), the necessary pages are
_at most_ 2 pages. If the system gets into the situation to fail to
allocate 2 contiguous pages, that's real the problem. I guess that
that kind of fragmentation problem would be solved with page migration
or something, especially nowadays devices are getting larger memories.

*1:
From a613c40d1b3d4fb1577cdb0807a74e8dbd08a3e6 Mon Sep 17 00:00:00 2001
From: Hiroshi Doyu <hdoyu@nvidia.com>
Date: Wed, 22 Aug 2012 16:25:54 +0300
Subject: [PATCH 1/1] ARM: dma-mapping: Use only kzalloc without vzalloc

Use only kzalloc for atomic allocation.

Signed-off-by: Hiroshi Doyu <hdoyu@nvidia.com>
---
 arch/arm/mm/dma-mapping.c |   10 ++--------
 1 files changed, 2 insertions(+), 8 deletions(-)

Comments

Minchan Kim Aug. 23, 2012, 3:49 a.m. UTC | #1 
On Wed, Aug 22, 2012 at 03:36:48PM +0200, Hiroshi Doyu wrote:
> Hi,
> 
> KyongHo Cho <pullip.cho@samsung.com> wrote @ Wed, 22 Aug 2012 14:47:00 +0200:
> 
> > vzalloc() call in __iommu_alloc_buffer() also causes BUG() in atomic context.
> 
> Right.
> 
> I've been thinking that kzalloc() may be enough here, since
> vzalloc() was introduced to avoid allocation failure for big chunk of
> memory, but I think that it's unlikely that the number of page array
> can be so big. So I propose to drop vzalloc() here, and just simply to
> use kzalloc only as below(*1).
> 
> For example, 
> 
> 1920(H) x 1080(W) x 4(bytes) ~= 8MiB
> 
> For 8 MiB buffer,
>   8(MiB) * 1024 = 8192(KiB)
>   8192(KiB) / 4(KiB/page) = 2048 pages
>   sizeof(struct page *) = 4 bytes
>   2048(pages) * 4(bytes/page) = 8192(bytes) = 8(KiB)
>   8(KiB) / 4(KiB/page) = 2 pages
> 
> If the above estimation is right(I hope;)), the necessary pages are
> _at most_ 2 pages. If the system gets into the situation to fail to
> allocate 2 contiguous pages, that's real the problem. I guess that
> that kind of fragmentation problem would be solved with page migration
> or something, especially nowadays devices are getting larger memories.

In atomic context, VM have no choice except relying on kswapd so
high order allocation can fail easily when memory fragementation
is high.
KyongHo Cho Aug. 23, 2012, 3:57 a.m. UTC | #2 
Hi.

We have faced with WQXGA(2560x1600) support and framebuffers become
dramatically larger.
Moreover, high resolution camera sensors also press memory use more than
the screen size.

However, I think that it is enough with your change because allocation
failure of several
contiguous pages also shows that the system don't have enough memory.

On Wed, Aug 22, 2012 at 10:36 PM, Hiroshi Doyu <hdoyu@nvidia.com> wrote:
> Hi,
>
> KyongHo Cho <pullip.cho@samsung.com> wrote @ Wed, 22 Aug 2012 14:47:00
+0200:
>
>> vzalloc() call in __iommu_alloc_buffer() also causes BUG() in atomic
context.
>
> Right.
>
> I've been thinking that kzalloc() may be enough here, since
> vzalloc() was introduced to avoid allocation failure for big chunk of
> memory, but I think that it's unlikely that the number of page array
> can be so big. So I propose to drop vzalloc() here, and just simply to
> use kzalloc only as below(*1).
>
> For example,
>
> 1920(H) x 1080(W) x 4(bytes) ~= 8MiB
>
> For 8 MiB buffer,
>   8(MiB) * 1024 = 8192(KiB)
>   8192(KiB) / 4(KiB/page) = 2048 pages
>   sizeof(struct page *) = 4 bytes
>   2048(pages) * 4(bytes/page) = 8192(bytes) = 8(KiB)
>   8(KiB) / 4(KiB/page) = 2 pages
>
> If the above estimation is right(I hope;)), the necessary pages are
> _at most_ 2 pages. If the system gets into the situation to fail to
> allocate 2 contiguous pages, that's real the problem. I guess that
> that kind of fragmentation problem would be solved with page migration
> or something, especially nowadays devices are getting larger memories.
>
> *1:
> From a613c40d1b3d4fb1577cdb0807a74e8dbd08a3e6 Mon Sep 17 00:00:00 2001
> From: Hiroshi Doyu <hdoyu@nvidia.com>
> Date: Wed, 22 Aug 2012 16:25:54 +0300
> Subject: [PATCH 1/1] ARM: dma-mapping: Use only kzalloc without vzalloc
>
> Use only kzalloc for atomic allocation.
>
> Signed-off-by: Hiroshi Doyu <hdoyu@nvidia.com>
> ---
>  arch/arm/mm/dma-mapping.c |   10 ++--------
>  1 files changed, 2 insertions(+), 8 deletions(-)
>
> diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
> index 4656c0f..d4f1cf2 100644
> --- a/arch/arm/mm/dma-mapping.c
> +++ b/arch/arm/mm/dma-mapping.c
> @@ -1083,10 +1083,7 @@ static struct page **__iommu_alloc_buffer(struct
device *dev, size_t size,
>         int count = size >> PAGE_SHIFT;
>         int array_size = count * sizeof(struct page *);
>
> -       if (array_size <= PAGE_SIZE)
> -               pages = kzalloc(array_size, gfp);
> -       else
> -               pages = vzalloc(array_size);
> +       pages = kzalloc(array_size, gfp);
>         if (!pages)
>                 return NULL;
>
> @@ -1107,10 +1104,7 @@ static struct page **__iommu_alloc_buffer(struct
device *dev, size_t size,
>
>         return pages;
>  error:
> -       if (array_size <= PAGE_SIZE)
> -               kfree(pages);
> -       else
> -               vfree(pages);
> +       kfree(pages);
>         return NULL;
>  }
>
> --
> 1.7.5.4
>
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@kvack.org.  For more info on Linux MM,
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> Don't email: <a hrefmailto:"dont@kvack.org"> email@kvack.org </a>
Marek Szyprowski Aug. 23, 2012, 5:58 a.m. UTC | #3 
Hello,

On Wednesday, August 22, 2012 3:37 PM Hiroshi Doyu wrote:

> KyongHo Cho <pullip.cho@samsung.com> wrote @ Wed, 22 Aug 2012 14:47:00 +0200:
> 
> > vzalloc() call in __iommu_alloc_buffer() also causes BUG() in atomic context.
> 
> Right.
> 
> I've been thinking that kzalloc() may be enough here, since
> vzalloc() was introduced to avoid allocation failure for big chunk of
> memory, but I think that it's unlikely that the number of page array
> can be so big. So I propose to drop vzalloc() here, and just simply to
> use kzalloc only as below(*1).

We already had a discussion about this, so I don't think it makes much sense to
change it back to kzalloc. This vmalloc() call won't hurt anyone. It should not
be considered a problem for atomic allocations, because no sane driver will try
to allocate buffers larger than a dozen KiB with GFP_ATOMIC flag. I would call
such try a serious bug, which we should not care here.

Best regards
Hiroshi Doyu Aug. 23, 2012, 6:15 a.m. UTC | #4 
Hi,

On Thu, 23 Aug 2012 07:58:34 +0200
Marek Szyprowski <m.szyprowski@samsung.com> wrote:

> Hello,
> 
> On Wednesday, August 22, 2012 3:37 PM Hiroshi Doyu wrote:
> 
> > KyongHo Cho <pullip.cho@samsung.com> wrote @ Wed, 22 Aug 2012 14:47:00 +0200:
> > 
> > > vzalloc() call in __iommu_alloc_buffer() also causes BUG() in atomic context.
> > 
> > Right.
> > 
> > I've been thinking that kzalloc() may be enough here, since
> > vzalloc() was introduced to avoid allocation failure for big chunk of
> > memory, but I think that it's unlikely that the number of page array
> > can be so big. So I propose to drop vzalloc() here, and just simply to
> > use kzalloc only as below(*1).
> 
> We already had a discussion about this, so I don't think it makes much sense to
> change it back to kzalloc. This vmalloc() call won't hurt anyone. It should not
> be considered a problem for atomic allocations, because no sane driver will try
> to allocate buffers larger than a dozen KiB with GFP_ATOMIC flag. I would call
> such try a serious bug, which we should not care here.

Ok, I've already sent v2 just now, where, instead of changing it back,
just with GFP_ATOMIC, kzalloc() would be selected, just in case. I guess
that this would be ok(a bit safer?)
Marek Szyprowski Aug. 23, 2012, 7:52 a.m. UTC | #5 
Hi Hiroshi,

On Thursday, August 23, 2012 8:15 AM Hiroshi Doyu wrote:

> On Thu, 23 Aug 2012 07:58:34 +0200
> Marek Szyprowski <m.szyprowski@samsung.com> wrote:
> 
> > Hello,
> >
> > On Wednesday, August 22, 2012 3:37 PM Hiroshi Doyu wrote:
> >
> > > KyongHo Cho <pullip.cho@samsung.com> wrote @ Wed, 22 Aug 2012 14:47:00 +0200:
> > >
> > > > vzalloc() call in __iommu_alloc_buffer() also causes BUG() in atomic context.
> > >
> > > Right.
> > >
> > > I've been thinking that kzalloc() may be enough here, since
> > > vzalloc() was introduced to avoid allocation failure for big chunk of
> > > memory, but I think that it's unlikely that the number of page array
> > > can be so big. So I propose to drop vzalloc() here, and just simply to
> > > use kzalloc only as below(*1).
> >
> > We already had a discussion about this, so I don't think it makes much sense to
> > change it back to kzalloc. This vmalloc() call won't hurt anyone. It should not
> > be considered a problem for atomic allocations, because no sane driver will try
> > to allocate buffers larger than a dozen KiB with GFP_ATOMIC flag. I would call
> > such try a serious bug, which we should not care here.
> 
> Ok, I've already sent v2 just now, where, instead of changing it back,
> just with GFP_ATOMIC, kzalloc() would be selected, just in case. I guess
> that this would be ok(a bit safer?)

I've posted some comments to v2. If you agree with my suggestion, no changes around
those vmalloc() calls will be needed.

Best regards
diff mbox

Patch

diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
index 4656c0f..d4f1cf2 100644
--- a/arch/arm/mm/dma-mapping.c
+++ b/arch/arm/mm/dma-mapping.c
@@ -1083,10 +1083,7 @@  static struct page **__iommu_alloc_buffer(struct device *dev, size_t size,
 	int count = size >> PAGE_SHIFT;
 	int array_size = count * sizeof(struct page *);
 
-	if (array_size <= PAGE_SIZE)
-		pages = kzalloc(array_size, gfp);
-	else
-		pages = vzalloc(array_size);
+	pages = kzalloc(array_size, gfp);
 	if (!pages)
 		return NULL;
 
@@ -1107,10 +1104,7 @@  static struct page **__iommu_alloc_buffer(struct device *dev, size_t size,
 
 	return pages;
 error:
-	if (array_size <= PAGE_SIZE)
-		kfree(pages);
-	else
-		vfree(pages);
+	kfree(pages);
 	return NULL;
 }