[PATCH/RFC] mm: add and use batched version of __tlb_remove_table()

[Nikita Yushchenko]

>> I currently don't have numbers for this patch taken alone. This patch
>> originates from work done some years ago to reduce cost of memory
>> accounting, and x86-only version of this patch was in virtuozzo/openvz
>> kernel since then. Other patches from that work have been upstreamed,
>> but this one was missed.
>>
>> Still it's obvious that release_pages() shall be faster that a loop
>> calling put_page() - isn't that exactly the reason why release_pages()
>> exists and is different from a loop calling put_page()?
> 
> Yep, but this patch does a bunch of stuff to some really hot paths.  It
> would be greatly appreciated if you could put in the effort to actually
> put some numbers behind this.  Plenty of weird stuff happens on
> computers that we suck at predicting.

I found the original report about high cost of memory accounting, and tried to repeat the test described 
there, with and without the patch.

The test is - run a script in 30 openvz containers in parallel, and measure average time per execution. 
Script is attached.

I'm getting measurable improvement in average msecs per execution: 15360 ms without patch, 15170 ms with 
patch. And this difference is reliably reproducible.

Nikita
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