On Wed, 2011-01-05 at 11:49 -0800, Linus Torvalds wrote: > 2011/1/5 James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>: > >> > >> No, we really can't do that. Most of the time, the kmap() is the only > >> way we access the page anyway, so flushing things would just be > >> stupid. Why waste time and energy on doing something pointless? > > > > It's hardly pointless. The kmap sets up an inequivalent alias in the > > cache. > > NO IT DOES NOT. Well, it does ... but not in this case because the page is freshly allocated (which I missed before) so it has no use cache colour yet. James > Stop arguing, when you are so wrong. > > kmap() does not create any aliases. For low-memory, it just returns > the physical address. No alias. And for high memory, there is no > equivalent low memory address to alias _with_. > > Now, when you actually mix multiple kmap's and you have a virtually > based cache, then the kmap's obviously need to flush that particular > page when switching between each other. But that has nothing to do > with the actual page being kmap'ed, it's entirely an internal issue > about the particular virtual memory area being re-used. And ARM (and > any other virtually based CPU) already does that in __kunmap_atomic(). > > But notice the case of the low-mem. And understand that you are WRONG > about the "inequivalent alias" thing. > > So I repeat: this has absolutely *NOTHING* to do with kmap(). Stop blathering. > > It's _purely_ an issue of vm_map_ram(). Nothing else. > > Linus -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
