On Sun, Nov 05, 2006 at 11:25:27PM +0200, Or Gerlitz wrote: > On 11/5/06, Roland Dreier <[EMAIL PROTECTED]> wrote: > > > I have mentioned this to Ralph in the past, just want to get ack/nak > > > on that from you: also on 64bit arch a block driver (eg SCSI LLD eg > > > SRP/iSER/etc) might get from higher level an SG whose pages are > > > **not** mapped into the kernel virtual address space. For example this > > > can happen with Direct I/O. > > > >No, I don't see how that could happen. Aren't all pages always mapped > >by the the kernel direct mapping on 64-bit architectures? > > I don't know exactly how this happens, but one of the comments i've > got from Christoph > on the iser code, is that one can't assume page_address(sg[i].page) > will not be NULL for SG passed to a SCSI LLD, i think Direct I/O is > one flow where this might happen.
That statement is indeed true. Only for GFP_KERNEL allocations you can assume page_address is valid, and the scatterlist passed to a SCSI LLDD can contain any type of pages. Currently on all 64bit architectures page_address works on all pages, but that's an implementation detail that could change any time and that you should not rely on. _______________________________________________ openib-general mailing list openib-general@openib.org http://openib.org/mailman/listinfo/openib-general To unsubscribe, please visit http://openib.org/mailman/listinfo/openib-general
