Re: [PATCH v2 2/2] dma-pool: Only allocate from CMA when in same memory zone
On Thu, Aug 06, 2020 at 01:50:29PM +0200, Nicolas Saenz Julienne wrote: > > The latter is pretty much what I expect, as we only support the default and > > per-device DMA CMAs. > > Fair enough, should I send a v3 with everything cleaned-up/rebased, or you'd > rather pick it up from your version? Please just resend the whole thing. ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
Re: [PATCH v2 2/2] dma-pool: Only allocate from CMA when in same memory zone
On Thu, 2020-08-06 at 07:18 +0200, Christoph Hellwig wrote: > On Tue, Aug 04, 2020 at 11:43:15AM +0200, Nicolas Saenz Julienne wrote: > > > Second I don't see the need (and actually some harm) in preventing > > > GFP_KERNEL > > > allocations from dipping into lower CMA areas - something that we did > > > support > > > before 5.8 with the single pool. > > > > My thinking is the least we pressure CMA the better, it's generally scarse, > > and > > it'll not grow as the atomic pools grow. As far as harm is concerned, we now > > check addresses for correctness, so we shouldn't run into problems. > > > > There is a potential case for architectures defining a default CMA but not > > defining DMA zones where this could be problematic. But isn't that just > > plain > > abusing CMA? If you need low memory allocations, you should be defining DMA > > zones. > > The latter is pretty much what I expect, as we only support the default and > per-device DMA CMAs. Fair enough, should I send a v3 with everything cleaned-up/rebased, or you'd rather pick it up from your version? signature.asc Description: This is a digitally signed message part ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
Re: [PATCH v2 2/2] dma-pool: Only allocate from CMA when in same memory zone
On Tue, Aug 04, 2020 at 11:43:15AM +0200, Nicolas Saenz Julienne wrote: > > Second I don't see the need (and actually some harm) in preventing > > GFP_KERNEL > > allocations from dipping into lower CMA areas - something that we did > > support > > before 5.8 with the single pool. > > My thinking is the least we pressure CMA the better, it's generally scarse, > and > it'll not grow as the atomic pools grow. As far as harm is concerned, we now > check addresses for correctness, so we shouldn't run into problems. > > There is a potential case for architectures defining a default CMA but not > defining DMA zones where this could be problematic. But isn't that just plain > abusing CMA? If you need low memory allocations, you should be defining DMA > zones. The latter is pretty much what I expect, as we only support the default and per-device DMA CMAs. ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
Re: [PATCH v2 2/2] dma-pool: Only allocate from CMA when in same memory zone
On Tue, 2020-08-04 at 08:06 +0200, Christoph Hellwig wrote: > On Mon, Aug 03, 2020 at 06:09:56PM +0200, Nicolas Saenz Julienne wrote: > > + if (IS_ENABLED(CONFIG_ZONE_DMA) && (gfp & GFP_DMA)) > > + return end <= DMA_BIT_MASK(zone_dma_bits); > > + if (IS_ENABLED(CONFIG_ZONE_DMA32) && (gfp & GFP_DMA32)) > > + return end <= DMA_BIT_MASK(32); > > + if (gfp & GFP_KERNEL) > > + return end > DMA_BIT_MASK(32); > > So the GFP_KERNEL one here looks weird. For one I don't think the if > line is needed at all, and it just confuses things. Yes, sorry, shoud've seen that. > Second I don't see the need (and actually some harm) in preventing GFP_KERNEL > allocations from dipping into lower CMA areas - something that we did support > before 5.8 with the single pool. My thinking is the least we pressure CMA the better, it's generally scarse, and it'll not grow as the atomic pools grow. As far as harm is concerned, we now check addresses for correctness, so we shouldn't run into problems. There is a potential case for architectures defining a default CMA but not defining DMA zones where this could be problematic. But isn't that just plain abusing CMA? If you need low memory allocations, you should be defining DMA zones. Regards, Nicolas signature.asc Description: This is a digitally signed message part ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
Re: [PATCH v2 2/2] dma-pool: Only allocate from CMA when in same memory zone
On Mon, Aug 03, 2020 at 06:09:56PM +0200, Nicolas Saenz Julienne wrote: > + if (IS_ENABLED(CONFIG_ZONE_DMA) && (gfp & GFP_DMA)) > + return end <= DMA_BIT_MASK(zone_dma_bits); > + if (IS_ENABLED(CONFIG_ZONE_DMA32) && (gfp & GFP_DMA32)) > + return end <= DMA_BIT_MASK(32); > + if (gfp & GFP_KERNEL) > + return end > DMA_BIT_MASK(32); So the GFP_KERNEL one here looks weird. For one I don't think the if line is needed at all, and it just confuses things. Second I don't see the need (and actually some harm) in preventing GFP_KERNEL allocations from dipping into lower CMA areas - something that we did support before 5.8 with the single pool. ___ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
