BAT mapping exported to user-space

Linh Dang linh at linhdang.home
Tue Jul 27 12:27:25 EST 2004

Dan Malek <dan at> wrote:
> On Jul 26, 2004, at 2:33 PM, Linh Dang wrote:
>> My understanding is:
>> - mmap(2) uses pages to map the device (my platform doesn't have large
>> page.)
> Yes, so?
>> - mapping a large address range (hundreds-of-megabytes) is much more
>> efficient with BATs than with pages.
> Depends upon your measurement of efficiency.
>> So, do you mean:
>> - mmap(2) can use BATs? or
> Not likely due to alignment and size constraints.
>> - the difference in performance is negligible between BATs and
>> pages when mapping an address range of 200MBs?
> If you can measure or are affected by the difference, there are many
> more things that will ensure your software will not work properly.

What do you mean by the above sentence?

- 200MB would need 51200 ptes. that means doubling the current number
  of ptes on my system.

- If using block mapping doesn't help that much then why would X make
  all the effort to grab MTRRs on X86?

- why would the kernel use BATs to map its memory?

Linh Dang

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