Messages in this thread | | | Date | Thu, 08 Apr 2004 15:19:51 -0700 | From | "Martin J. Bligh" <> | Subject | Re: -mmX 4G patches feedback [numbers: how much performance impact] |
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--On Thursday, April 08, 2004 23:59:46 +0200 Andrea Arcangeli <andrea@suse.de> wrote:
> On Wed, Apr 07, 2004 at 11:24:16PM -0700, Martin J. Bligh wrote: >> Instead of fiddling with tuning knobs, I'd prefer to just do the UKVA >> idea I've proposed before, and let each process have their own pagetables >> mapped permanently ;-) > > that will have you pay for pte-highmem even in non-highmem machines. > I'm always been against your above idea ;) It can speedup mmap a bit for > some uncommon case but I believe your slowdown comes from the page faults after > exeve and startup not from mmap with the kernel compile, and worst of > all for non-highmem too (no sysctl or tuning knob can save you then). > Amittedly some mmap intensive workload can get a slight speedup compared > to pte-highmem but I don't think it's common and it has the potential of > slowing down the page faults especially in short lived tasks even w/o > highmem.
You mean the page-faults for the pagetable mappings themselves? I wouldn't have thought that'd make an impact - at least I don't see how it could be worse than pte_highmem. And as we could make it conditional on highmem anyway (or even CONFIG_64GB, I'm pretty sure 4GB machines don't need it), I don't think it matters (ie you'd just turn it on instead of pte_highmem).
But you're right, we do need to take that into consideration.
> What I found attractive was the persistent kmap in userspace, but that > idea breaks with threading, and Andrew found another way that is to make > the page fault interruptible so it doesn't seem very worthwhile anymore > even w/o threading.
Yeah, I've given up on that one ;-) The main use for it was pagetables anyway, and we can do that without the threading problems.
M.
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