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Re: shared pagetable benchmarking
On Fri, 27 Dec 2002, Andrew Morton wrote:
>
> I think we can do a few things still in the 2.6 context. The fact that
> my "apply seventy patches with patch-scripts" test takes 350,000 pagefaults
> in 13 seconds makes one go "hmm".
Hmm.. Whatever happened to the MAP_POPULATE tests?
The current "filemap_populate()" function is extremely stupid (it takes
advantage neither of the locality of the page tables _nor_ of the radix
tree layout), but even so it would probably be a win to pre-populate at
mmap time.
But having a better "populate()" function that actually does multiple
pages at once by just accessing the radix trees and page table trees
directly should really be very low-overhead for the normal case, and be a
_big_ win in avoiding page faults.
Even with the existing stupid populate function, it might be interesting
seeing what would happen just from doing something silly like
===== arch/i386/kernel/sys_i386.c 1.10 vs edited =====
--- 1.10/arch/i386/kernel/sys_i386.c Sat Dec 21 08:24:45 2002
+++ edited/arch/i386/kernel/sys_i386.c Fri Dec 27 19:08:30 2002
@@ -54,6 +54,8 @@
file = fget(fd);
if (!file)
goto out;
+ if (prot & PROT_EXEC)
+ flags |= MAP_POPULATE | MAP_NONBLOCK;
}
down_write(¤t->mm->mmap_sem);
(yeah, yeah, and maybe do the same in binfmt_elf.c too)
Linus
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