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Date: Fri, 8 Aug 2008 13:25:59 -0700 From: "Grant Grundler" <grundler@...gle.com> To: "Stefan Richter" <stefanr@...6.in-berlin.de> Cc: linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: Scatter-gather segment merges by IOMMU? On Fri, Aug 8, 2008 at 12:44 PM, Stefan Richter <stefanr@...6.in-berlin.de> wrote: > Hi all, > > the block layer usually tries to merge s/g segments if consecutive segments > combined fit into the queue's max_segment_size. When such a scatter gather > list is DMA-mapped, can it happen that an IOMMU collapses the elements even > further, so that sg_dma_len() of a DMA-mapped s/g segment exceeds > max_segment_size? I don't see how. The IOMMU code only collapses the "physical" mappings and does not add new elements to the SG list. ergo sg_dma_len() shouldn't change. grant > > As I understood some discussions in the past, this could indeed happen, > which is a nuisance. But I may have misunderstood something, or something > may have changed in the meantime... > -- > Stefan Richter > -=====-==--- =--- -=--- > http://arcgraph.de/sr/ > -- > To unsubscribe from this list: send the line "unsubscribe linux-scsi" in > the body of a message to majordomo@...r.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.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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