On Wed, 16 Jul 2008, FUJITA Tomonori wrote: > On Tue, 15 Jul 2008 11:46:46 -0400 (EDT) > Mikulas Patocka <mpatocka@xxxxxxxxxx> wrote: > > > >> Even if we fix it now, the question is: how long it will stay fixed? Until > > >> someone makes another change to struct device that restricts boundaries on > > >> some wacky hardware. > > > > > > I'm not sure how the boundary restriction of a device can break > > > the VMERGE accounting. > > > > Because block layer code doesn't know anything about the device, pci > > access restrictions and so on. > > Not true, the block layer knows about the device restrictions like DMA > boundary. > > But it's not the point here because the boundary restriction doesn't > matter for the VMERGE accounting. An IOMMU just returns an error if it > can't allocate an I/O space fit for the device restrictions. > > > Please give me an example how the boundary restriction of a device can > break the VMERGE accounting and an IOMMU if you aren't still sure. You have dma_get_seg_boundary and dma_get_max_seg_size. On sparc64, adding one of these broken VMERGE accounting (the VMERGE didn't happen past 64-kb boundary and bio layer thought that VMERGE would be possible). And if you fix this case, someone will break it again, sooner or later, by adding new restriction. Mikulas -- To unsubscribe from this list: 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
