On Wed, Apr 06, 2016 at 10:51:40AM +0800, Ming Lei wrote: > On Wed, Apr 6, 2016 at 10:40 AM, Kent Overstreet > <kent.overstreet@xxxxxxxxx> wrote: > > On Wed, Apr 06, 2016 at 10:37:05AM +0800, Ming Lei wrote: > >> On Wed, Apr 6, 2016 at 10:34 AM, Kent Overstreet > >> <kent.overstreet@xxxxxxxxx> wrote: > >> > On Wed, Apr 06, 2016 at 10:30:22AM +0800, Ming Lei wrote: > >> >> Now limit.max_segments is for limiting segments from hw view, one this > >> >> segment may include lots of pages/bvecs. > >> >> > >> >> The current bio_clone() issue is that we can't clone from one bio which > >> >> includes more than 256 bvecs, maybe all these 256 bvecs belong to > >> >> one same hw segment. > >> > > >> > So the distinction is purely a post multipage bvec thing? > >> > >> Even after multipage bvec is applied, the limit for max bvecs is still needed > >> for some cases like bio bounce, in which bio_clone() need to > >> clone single page bvec. > > > > s/max bvecs/max pages/? > > Exactly, :-) > > > > > What I meant is that until we have multipage bvecs, unless I'm missing something > > max_segments is exactly what we want. After multipage bvecs, things do get more > > Yes, but now we need to fix current issue and backport the fix. Given bio > bounce isn't easy to fix, not like other users of bio_clone, I think > we still need > to apply the max pages limit globally, what do you think of it? Ugh, yeah bouncing is an issue, with that it's most of the drivers. Ok, yeah I guess the global limit makes sense for now. Please add a giant comment explaining why the global limit is there, precisely what it's needed for and that we'd like to get rid of it. -- To unsubscribe from this list: send the line "unsubscribe linux-block" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
