On Wed, 2006-03-01 at 11:00 -0500, Douglas Gilbert wrote: > So the maximum data carrying size of a scatter gather list > is not deterministic? Is the worst case (page_size * SG_ALL)? Correct, essentially. The size is bounded by the number of elements, but there's no fixed size for those elements unless clustering is disabled, in which case PAGE_SIZE is the fixed size. However, in most machines fragmentation effects will cause a certain amount of unpredictability in the true size of the request. And, obviously, for IOMMU machines, the block layer limits are about the only factor. However, having users rely on unpredictable effects like physical merging or the presence of an iommu isn't really best practice, so practially, the user must assume PAGE_SIZE * SG_ALL (assming the actual HBA uses SG_ALL, which not all do) James - : send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
