Re: [patch] dma-pool: warn when coherent pool is depleted

Re: [patch] dma-pool: warn when coherent pool is depleted

[Guenter Roeck]

On Sun, Jun 21, 2020 at 01:43:02PM -0700, David Rientjes wrote:
> When a DMA coherent pool is depleted, allocation failures may or may not
> get reported in the kernel log depending on the allocator.
> 
> The admin does have a workaround, however, by using coherent_pool= on the
> kernel command line.
> 
> Provide some guidance on the failure and a recommended minimum size for
> the pools (double the size).
> 
> Signed-off-by: David Rientjes <rientjes@google.com>

Tested-by: Guenter Roeck <linux@roeck-us.net>

Also confirmed that coherent_pool=256k works around the crash
I had observed.

Guenter

> ---
>  kernel/dma/pool.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/dma/pool.c b/kernel/dma/pool.c
> --- a/kernel/dma/pool.c
> +++ b/kernel/dma/pool.c
> @@ -239,12 +239,16 @@ void *dma_alloc_from_pool(struct device *dev, size_t size,
>  	}
>  
>  	val = gen_pool_alloc(pool, size);
> -	if (val) {
> +	if (likely(val)) {
>  		phys_addr_t phys = gen_pool_virt_to_phys(pool, val);
>  
>  		*ret_page = pfn_to_page(__phys_to_pfn(phys));
>  		ptr = (void *)val;
>  		memset(ptr, 0, size);
> +	} else {
> +		WARN_ONCE(1, "DMA coherent pool depleted, increase size "
> +			     "(recommended min coherent_pool=%zuK)\n",
> +			  gen_pool_size(pool) >> 9);
>  	}
>  	if (gen_pool_avail(pool) < atomic_pool_size)
>  		schedule_work(&atomic_pool_work);
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Re: [patch] dma-pool: warn when coherent pool is depleted

[David Rientjes via iommu]

On Sun, 21 Jun 2020, Guenter Roeck wrote:

> > When a DMA coherent pool is depleted, allocation failures may or may not
> > get reported in the kernel log depending on the allocator.
> > 
> > The admin does have a workaround, however, by using coherent_pool= on the
> > kernel command line.
> > 
> > Provide some guidance on the failure and a recommended minimum size for
> > the pools (double the size).
> > 
> > Signed-off-by: David Rientjes <rientjes@google.com>
> 
> Tested-by: Guenter Roeck <linux@roeck-us.net>
> 
> Also confirmed that coherent_pool=256k works around the crash
> I had observed.
> 

Thanks Guenter.  Christoph, does it make sense to apply this patch since 
there may not be an artifact left behind in the kernel log on allocation 
failure by the caller?

> Guenter
> 
> > ---
> >  kernel/dma/pool.c | 6 +++++-
> >  1 file changed, 5 insertions(+), 1 deletion(-)
> > 
> > diff --git a/kernel/dma/pool.c b/kernel/dma/pool.c
> > --- a/kernel/dma/pool.c
> > +++ b/kernel/dma/pool.c
> > @@ -239,12 +239,16 @@ void *dma_alloc_from_pool(struct device *dev, size_t size,
> >  	}
> >  
> >  	val = gen_pool_alloc(pool, size);
> > -	if (val) {
> > +	if (likely(val)) {
> >  		phys_addr_t phys = gen_pool_virt_to_phys(pool, val);
> >  
> >  		*ret_page = pfn_to_page(__phys_to_pfn(phys));
> >  		ptr = (void *)val;
> >  		memset(ptr, 0, size);
> > +	} else {
> > +		WARN_ONCE(1, "DMA coherent pool depleted, increase size "
> > +			     "(recommended min coherent_pool=%zuK)\n",
> > +			  gen_pool_size(pool) >> 9);
> >  	}
> >  	if (gen_pool_avail(pool) < atomic_pool_size)
> >  		schedule_work(&atomic_pool_work);
> 
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Re: [patch] dma-pool: warn when coherent pool is depleted

[Christoph Hellwig]

On Sat, Jun 27, 2020 at 09:25:21PM -0700, David Rientjes wrote:
> Thanks Guenter.  Christoph, does it make sense to apply this patch since 
> there may not be an artifact left behind in the kernel log on allocation 
> failure by the caller?

Sorry, this fell through the cracks.  I've added it to the dma-mapping
tree now.
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[patch] dma-pool: warn when coherent pool is depleted

[David Rientjes via iommu]

When a DMA coherent pool is depleted, allocation failures may or may not
get reported in the kernel log depending on the allocator.

The admin does have a workaround, however, by using coherent_pool= on the
kernel command line.

Provide some guidance on the failure and a recommended minimum size for
the pools (double the size).

Signed-off-by: David Rientjes <rientjes@google.com>
---
 kernel/dma/pool.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/kernel/dma/pool.c b/kernel/dma/pool.c
--- a/kernel/dma/pool.c
+++ b/kernel/dma/pool.c
@@ -239,12 +239,16 @@ void *dma_alloc_from_pool(struct device *dev, size_t size,
 	}
 
 	val = gen_pool_alloc(pool, size);
-	if (val) {
+	if (likely(val)) {
 		phys_addr_t phys = gen_pool_virt_to_phys(pool, val);
 
 		*ret_page = pfn_to_page(__phys_to_pfn(phys));
 		ptr = (void *)val;
 		memset(ptr, 0, size);
+	} else {
+		WARN_ONCE(1, "DMA coherent pool depleted, increase size "
+			     "(recommended min coherent_pool=%zuK)\n",
+			  gen_pool_size(pool) >> 9);
 	}
 	if (gen_pool_avail(pool) < atomic_pool_size)
 		schedule_work(&atomic_pool_work);
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