Messages in this thread | | | Date | Sun, 23 May 2004 19:39:52 -0700 | From | William Lee Irwin III <> | Subject | Re: 4g/4g for 2.6.6 |
| |
On Sun, May 23, 2004 at 01:32:19PM -0700, Linus Torvalds wrote: > Quite frankly, a number of us are hoping that we can make them > unnecessary. The cost of the 4g/4g split is absolutely _huge_ on some > things, including basic stuff like kernel compiles. > The only valid reason for the 4g split is that the VM doesn't always > behave well with huge amounts of highmem. The anonvma stuff in 2.6.7-pre1 > is hoped to make that much less of an issue. > Personally, if we never need to merge 4g for real, I'll be really really > happy. I see it as a huge ugly hack.
The performance can be improved by using a u area to store and map things like vmas, kernel stacks, pagetables, file handles and descriptor tables, and the like with supervisor privileges in the same set of pagetables as the user context so that system calls may be serviced without referencing the larger global kernel data area, which would require the %cr3 reload. This does, however, seem at odds with Linux' design in a number of respects, e.g. vmas etc. are on lists containing elements belonging to different contexts. I suspect kernels doing this would have to architect their page replacement algorithms and truncate() semantics so as to avoid these out-of-context accesses or otherwise suffer these operations being inefficient.
-- wli - 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/
| |