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7f9e5c48c1
By default, each device is assumed to be able only handle 64 KB chunks during DMA. By giving the segment size a larger value, the block layer will coalesce more S/G entries together for SRP, allowing larger requests with the same sg_tablesize setting. The block layer is the only direct user of it, though a few IOMMU drivers reference it as well for their *_map_sg coalescing code. pci-gart_64 on x86, and a smattering on on sparc, powerpc, and ia64. Since other IB protocols could potentially see larger segments with this, let's check those: - iSER is fine, because you limit your maximum request size to 512 KB, so we'll never overrun the page vector in struct iser_page_vec (128 entries currently). It is independent of the DMA segment size, and handles multi-page segments already. - IPoIB is fine, as it maps each page individually, and doesn't use ib_dma_map_sg(). - RDS appears to do the right thing and has no dependencies on DMA segment size, but I don't claim to have done a complete audit. - NFSoRDMA and 9p are OK -- they do not use ib_dma_map_sg(), so they doesn't care about the coalescing. - Lustre's ko2iblnd does not care about coalescing -- it properly walks the returned sg list. This patch ups the value on Mellanox hardware to 1 GB, which matches reported firmware limits on mlx4. Signed-off-by: David Dillow <dillowda@ornl.gov> Signed-off-by: Roland Dreier <roland@purestorage.com> |
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