James Bottomley wrote: > On Wed, 2006-03-01 at 16:29 +0100, Jens Axboe wrote: > >>Strictly speaking, the clustering bit is unrelated. I seem to recall >>Gerard years ago talking about some sym chips that did not like >>clustering, hence it was disabled. > > > Yes, I remember that too ... I've never been able to find out which > chip, though ... the scripts all seem happily coded for variable size sg > segments. > > However, given the new way 2.6 does memory allocations, > ENABLE_CLUSTERING will probably make quite a difference to the size of > the sg list ... since we try to allocate contiguous pages, physical > merging becomes much more of a possibility (I think I last measured it > at around 30% of all SG tables, as opposed to <1% with the old > allocation method). James, So the maximum data carrying size of a scatter gather list is not deterministic? Is the worst case (page_size * SG_ALL)? Doug Gilbert - : 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
