Re: [00/41] Large Blocksize Support V7 (adds memmap support)

On Tue, Sep 11, 2007 at 05:04:41PM -0700, Christoph Lameter wrote:
I would think that your approach would be slower since you always have to
populate 1 << N ptes when mmapping a file? Plus there is a lot of wastage

I don't have to populate them, I could just map one at time. The only
reason I want to populate every possible pte that could map that page
(by checking vma ranges) is to _improve_ performance by decreasing the
number of page faults of an order of magnitude. Then with the 62th bit
after NX giving me a 64k tlb, I could decrease the frequency of the
tlb misses too.

of memory because even a file with one character needs an order N page? So
there are less pages available for the same workload.

This is a known issue. The same is true for ppc64 64k. If that really
is an issue, that may need some generic solution with tail packing.

Then you are breaking mmap assumptions of applications becaused the order
N kernel will no longer be able to map 4k pages. You likely need a new
binary format that has pages correctly aligned. I know that we would need
one on IA64 if we go beyond the established page sizes.

No you misunderstood the whole design. My patch will be 100% backwards
compatible in all respects. If I could break backwards compatibility
70% of the complexity would go away...
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