From: Nicolas Saenz Julienne <nsaenzjulienne@suse.de> To: Christoph Hellwig <hch@lst.de> Cc: amit.pundir@linaro.org, linux-kernel@vger.kernel.org, Marek Szyprowski <m.szyprowski@samsung.com>, Robin Murphy <robin.murphy@arm.com>, rientjes@google.com, jeremy.linton@arm.com, linux-rpi-kernel@lists.infradead.org, iommu@lists.linux-foundation.org Subject: Re: [PATCH v2 2/2] dma-pool: Only allocate from CMA when in same memory zone Date: Tue, 04 Aug 2020 11:43:15 +0200 [thread overview] Message-ID: <e0b2a00c8cf86cb1a91804942d35c9d4b98e9f9f.camel@suse.de> (raw) In-Reply-To: <20200804060633.GA7368@lst.de> [-- Attachment #1: Type: text/plain, Size: 1279 bytes --] 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 [-- Attachment #2: This is a digitally signed message part --] [-- Type: application/pgp-signature, Size: 488 bytes --]
WARNING: multiple messages have this Message-ID (diff)
From: Nicolas Saenz Julienne <nsaenzjulienne@suse.de> To: Christoph Hellwig <hch@lst.de> Cc: amit.pundir@linaro.org, linux-kernel@vger.kernel.org, jeremy.linton@arm.com, iommu@lists.linux-foundation.org, linux-rpi-kernel@lists.infradead.org, rientjes@google.com, Robin Murphy <robin.murphy@arm.com> Subject: Re: [PATCH v2 2/2] dma-pool: Only allocate from CMA when in same memory zone Date: Tue, 04 Aug 2020 11:43:15 +0200 [thread overview] Message-ID: <e0b2a00c8cf86cb1a91804942d35c9d4b98e9f9f.camel@suse.de> (raw) In-Reply-To: <20200804060633.GA7368@lst.de> [-- Attachment #1.1: Type: text/plain, Size: 1279 bytes --] 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 [-- Attachment #1.2: This is a digitally signed message part --] [-- Type: application/pgp-signature, Size: 488 bytes --] [-- Attachment #2: Type: text/plain, Size: 156 bytes --] _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
next prev parent reply other threads:[~2020-08-04 9:43 UTC|newest] Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-08-03 16:09 [PATCH v2 0/2] dma-pool fixes Nicolas Saenz Julienne 2020-08-03 16:09 ` Nicolas Saenz Julienne 2020-08-03 16:09 ` [PATCH v2 1/2] dma-pool: fix coherent pool allocations for IOMMU mappings Nicolas Saenz Julienne 2020-08-03 16:09 ` Nicolas Saenz Julienne 2020-08-03 16:09 ` [PATCH v2 2/2] dma-pool: Only allocate from CMA when in same memory zone Nicolas Saenz Julienne 2020-08-03 16:09 ` Nicolas Saenz Julienne 2020-08-04 6:06 ` Christoph Hellwig 2020-08-04 6:06 ` Christoph Hellwig 2020-08-04 9:43 ` Nicolas Saenz Julienne [this message] 2020-08-04 9:43 ` Nicolas Saenz Julienne 2020-08-06 5:18 ` Christoph Hellwig 2020-08-06 5:18 ` Christoph Hellwig 2020-08-06 11:50 ` Nicolas Saenz Julienne 2020-08-06 11:50 ` Nicolas Saenz Julienne 2020-08-06 13:55 ` Christoph Hellwig 2020-08-06 13:55 ` Christoph Hellwig
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