Messages in this thread | | | Date | Sat, 30 Mar 2002 20:44:44 +0100 | From | Andrea Arcangeli <> | Subject | Re: Backport of Ingo/Arjan highpte to 2.4.18 (+O1 scheduler) |
| |
On Fri, Mar 29, 2002 at 02:49:07PM -0800, Martin J. Bligh wrote: > > I'm not considering to drop pte-highmem from 2.4 and to only support the > > user-fixmaps in 2.5 because it is a showstopper bugfix for lots of > > important users that definitely cannot wait 2.6. I'm also not > > considering backporting the user-fixmaps because that would be a quite > > invasive change messing also with the alignment of the user stack (I > > know it could stay into kernel space, but right after the user stack it > > will be more optimized and cleaner/simpler, so I prefer to put the few > > virtual pages there). > > Can you explain the problem with the aligment of the user stack? I can't > see what the problem is here .... and we need to start thinking about how > to fix it if you've seen a problem that we haven't ....
the user stack never started on a non power of two, so far, so some buggy app may do assumptions on that, and bugs could trigger than. No app should break in theory. If somebody is doing a map fixed near the stack using a and-mask (instead of a minus) on %esp to calculate the offset of the map-fixed, that could break if we eat a copule of virtual pages of stack. I triggered something related when I was using a bit larger heap-stack-gap, I know there are apps putting mappings very near the stack (the one I've in mind isn't even open source so I don't know how it chooses the address), but most probably correctly none of them makes assumption on the alignment of the top of the stack, so it's should be safe, but you know you never know :). Also given the complexity of the patch, and also given it's definitely not necessary in 2.4 just to get the scalability bit I recommend it for 2.5 only (my new scalable pte-highmem using atomics in the fast paths and persistent in the slow paths where 2.5 is also currently broken is just working just fine on top of pre4). I was ready to release it today (just running for one day of stress testing), but pre5 came out so I'll have to spend some more hour to slowly resync and rediff.
Andrea - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |