On 8/1/07, Alan Cox <[EMAIL PROTECTED]> wrote: > On Wed, 1 Aug 2007 15:33:58 +0200 > Andrea Arcangeli <[EMAIL PROTECTED]> wrote: > > Tweaking kernel ptes is prohibitive during clone() because that's > > kernel memory and it would require a flush tlb all with IPIs that > > won't scale (IPIs are really the blocker) > > Agreed - except when doing debug work then its an acceptable cost. You > still have to sort the debug side out because you are going to fault the > kernel stack which will probably then cause a triple fault and reboot on > the spot.
I was assuming debugging work, yes. I was also thinking it wouldn't be done at clone() time, but mapped (on a single CPU) at the time of a context switch. It would eliminate IPI, but would probably make the rest of the TLB handling much too ugly to contemplate. As an alternative, could the TLB flush and associated IPI be deferred until the process migrates? First migration would trigger flush/IPI, further migration would be as now, no? I'd happily run it with various dm/md layers underneath On 8/1/07, Denis Vlasenko <[EMAIL PROTECTED]> wrote: > Hmm, neat. Why do you need to _allocate second page_ at all? > Just mark it "not present"... Because the kernel mapping covers all physical memory contiguously, so if the page isn't allocated, it could be used by a kernel data structure you need to access. Same reason the kernel stack has to be contiguous pages. Well, for non-highmem at least. Either way, you don't want to mark an in-use page as inaccessable, you never know what's under there. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
