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SubjectRe: 2G memory split
Jens Axboe wrote:

>On Tue, Jan 10 2006, Jeff V. Merkey wrote:
>
>
>>Alan Cox wrote:
>>
>>
>>
>>>On Maw, 2006-01-10 at 09:56 -0700, Jeff V. Merkey wrote:
>>>
>>>
>>>
>>>
>>>>RH ES uses 4:4 which is ideal and superior to this hack.
>>>>
>>>>
>>>>
>>>>
>>>Its a non trivial trade-off. 4/4 lets you run very large physical memory
>>>systems much more efficiently than usual but you pay a cost on syscalls
>>>and some other events when using the majority of processors. The 4/4
>>>tricks also give most emulations (eg Qemu) serious heartburn trying to
>>>emulate %cr3 reloading via mmap and other interfaces with high overhead
>>>in relative terms.
>>>
>>>Of course AMD64 kind of shot the problem in the head once and for all.
>>>
>>>
>>>
>>>
>>>
>>Yep, they sure did. Seriously, the 4:4 option should also be present
>>along with 3:1 and 2:2
>>splits. You should merge your RH work into this patch and allow both.
>>It would save me one less
>>patch to maintain off the tree.
>>
>>
>
>You can't compare the two patches, saying that 4:4 should go in because
>configurable page offsets is merged is nonsense.
>
>Note that I'm not advocating against 4:4 as such, I have no real
>oppinion on that. It has its uses for sure, while it comes with a cost
>for others.
>
>
>
I agree and I appreciate your recognizing this. As it stands, if I need
4:4 I just ship on ES3 and ES4. the 3:1
patch in the standard kernel is a very good thing, and you are to be
commended for finally getting it in.

P.S. Your bio stuff works great.

Jeff
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