Messages in this thread | | | Date | Sat, 30 Jun 2007 00:11:38 +0100 | From | Alan Cox <> | Subject | Re: [PATCH] Containment measures for slab objects on scatter gather lists |
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> DMA to or from memory should be done via the DMA mapping API. If we're > DMAing to/from a limited range within a page, either we should be using > dma_map_single(), or dma_map_page() with an appropriate offset and size.
If those ranges overlap a cache line then the dma mapping API will not save your backside.
On a system with a 32 byte cache granularity what happens if you get two dma mapping calls for x and x+16. Right now the thing that avoids this occurring is that the allocators don't pack stuff in that hard so x+16 always belongs to the same driver and we can hope driver authors are sensible
> sizes, but they do happen. We handle this on ARM by writing back > the overlapped lines and invalidating the rest before the DMA operation > commences, and hope that the overlapped lines aren't touched for the > duration of the DMA.)
The combination of "hope" and "DMA" isn't a good one for stable system design. In this situation we should be waving large red flags - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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