Re: [PATCH] dma-direct: document the zone selection logic
On Mon, 2018-10-08 at 09:03 +0200, Christoph Hellwig wrote: > Ben, does this resolve your issues with the confusing zone selection? The comment does make things a tad clearer yes :) Thanks ! Cheers, Ben. > On Mon, Oct 01, 2018 at 01:10:16PM -0700, Christoph Hellwig wrote: > > What we are doing here isn't quite obvious, so add a comment explaining > > it. > > > > Signed-off-by: Christoph Hellwig > > --- > > kernel/dma/direct.c | 9 - > > 1 file changed, 8 insertions(+), 1 deletion(-) > > > > diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c > > index ba6f5956a291..14b966e2349a 100644 > > --- a/kernel/dma/direct.c > > +++ b/kernel/dma/direct.c > > @@ -84,7 +84,14 @@ static gfp_t __dma_direct_optimal_gfp_mask(struct device > > *dev, u64 dma_mask, > > else > > *phys_mask = dma_to_phys(dev, dma_mask); > > > > - /* GFP_DMA32 and GFP_DMA are no ops without the corresponding zones: */ > > + /* > > +* Optimistically try the zone that the physicall address mask falls > > +* into first. If that returns memory that isn't actually addressable > > +* we will fallback to the next lower zone and try again. > > +* > > +* Note that GFP_DMA32 and GFP_DMA are no ops without the corresponding > > +* zones. > > +*/ > > if (*phys_mask <= DMA_BIT_MASK(ARCH_ZONE_DMA_BITS)) > > return GFP_DMA; > > if (*phys_mask <= DMA_BIT_MASK(32)) > > -- > > 2.19.0 > > > > ___ > > iommu mailing list > > iommu@lists.linux-foundation.org > > https://lists.linuxfoundation.org/mailman/listinfo/iommu > > ---end quoted text--- ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
Re: [PATCH] dma-direct: document the zone selection logic
Ben, does this resolve your issues with the confusing zone selection? On Mon, Oct 01, 2018 at 01:10:16PM -0700, Christoph Hellwig wrote: > What we are doing here isn't quite obvious, so add a comment explaining > it. > > Signed-off-by: Christoph Hellwig > --- > kernel/dma/direct.c | 9 - > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c > index ba6f5956a291..14b966e2349a 100644 > --- a/kernel/dma/direct.c > +++ b/kernel/dma/direct.c > @@ -84,7 +84,14 @@ static gfp_t __dma_direct_optimal_gfp_mask(struct device > *dev, u64 dma_mask, > else > *phys_mask = dma_to_phys(dev, dma_mask); > > - /* GFP_DMA32 and GFP_DMA are no ops without the corresponding zones: */ > + /* > + * Optimistically try the zone that the physicall address mask falls > + * into first. If that returns memory that isn't actually addressable > + * we will fallback to the next lower zone and try again. > + * > + * Note that GFP_DMA32 and GFP_DMA are no ops without the corresponding > + * zones. > + */ > if (*phys_mask <= DMA_BIT_MASK(ARCH_ZONE_DMA_BITS)) > return GFP_DMA; > if (*phys_mask <= DMA_BIT_MASK(32)) > -- > 2.19.0 > > ___ > iommu mailing list > iommu@lists.linux-foundation.org > https://lists.linuxfoundation.org/mailman/listinfo/iommu ---end quoted text--- ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
Re: [PATCH] dma-direct: document the zone selection logic
On 10/1/18 1:10 PM, Christoph Hellwig wrote: > What we are doing here isn't quite obvious, so add a comment explaining > it. > > Signed-off-by: Christoph Hellwig > --- > kernel/dma/direct.c | 9 - > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c > index ba6f5956a291..14b966e2349a 100644 > --- a/kernel/dma/direct.c > +++ b/kernel/dma/direct.c > @@ -84,7 +84,14 @@ static gfp_t __dma_direct_optimal_gfp_mask(struct device > *dev, u64 dma_mask, > else > *phys_mask = dma_to_phys(dev, dma_mask); > > - /* GFP_DMA32 and GFP_DMA are no ops without the corresponding zones: */ > + /* > + * Optimistically try the zone that the physicall address mask falls physical > + * into first. If that returns memory that isn't actually addressable > + * we will fallback to the next lower zone and try again. > + * > + * Note that GFP_DMA32 and GFP_DMA are no ops without the corresponding > + * zones. > + */ > if (*phys_mask <= DMA_BIT_MASK(ARCH_ZONE_DMA_BITS)) > return GFP_DMA; > if (*phys_mask <= DMA_BIT_MASK(32)) > thanks for the documentation. -- ~Randy ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
[PATCH] dma-direct: document the zone selection logic
What we are doing here isn't quite obvious, so add a comment explaining it. Signed-off-by: Christoph Hellwig --- kernel/dma/direct.c | 9 - 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c index ba6f5956a291..14b966e2349a 100644 --- a/kernel/dma/direct.c +++ b/kernel/dma/direct.c @@ -84,7 +84,14 @@ static gfp_t __dma_direct_optimal_gfp_mask(struct device *dev, u64 dma_mask, else *phys_mask = dma_to_phys(dev, dma_mask); - /* GFP_DMA32 and GFP_DMA are no ops without the corresponding zones: */ + /* +* Optimistically try the zone that the physicall address mask falls +* into first. If that returns memory that isn't actually addressable +* we will fallback to the next lower zone and try again. +* +* Note that GFP_DMA32 and GFP_DMA are no ops without the corresponding +* zones. +*/ if (*phys_mask <= DMA_BIT_MASK(ARCH_ZONE_DMA_BITS)) return GFP_DMA; if (*phys_mask <= DMA_BIT_MASK(32)) -- 2.19.0 ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
