memory with __get_free_pages and disabling caching

[Kumar Gala]

On Mar 24, 2006, at 1:13 PM, Kallol Biswas wrote:

>
> We have a little endian device on a PPC 440GX based system.
> The descriptors need to be swapped. With E bit turned on we can  
> save swapping time.

What's the device and what bus is it on?  Are you writing a standard  
kernel driver for it?

> May be all the pages with _get_free_page already are mapped with  
> large tlb entry.
>
> How about making a window (ptes) like consistent memory?
>
> -----Original Message-----
> From: Benjamin Herrenschmidt [mailto:benh at kernel.crashing.org]
> Sent: Thursday, March 23, 2006 7:06 PM
> To: Kallol Biswas
> Cc: linuxppc-dev at ozlabs.org
> Subject: Re: memory with __get_free_pages and disabling caching
>
> On Thu, 2006-03-23 at 18:15 -0800, Kallol Biswas wrote:
>> Hello,
>>        Is there an easy way to set page table attributes for the
>> memory returned by __get_free_pages()?
>>
>> I need to be able to turn off caching and turn on E bit for these
>> pages.
>
> The Evil bit ? heh ! what are you trying to do ? here ... you can  
> always create a virtual mapping to those pages with different  
> attributes but that's nor recommended as some processors will shoke  
> pretty badly if you end up with both cacheable and non-cacheable  
> mappings for the same page.
> However, it's not always possible to unmap the initial mapping  
> since it's common to use things like large pages, BATs, large TLB  
> entries etc... to map kernel memory..
>
>> I tried to walk through the page tables data structures to get the
>> pte, but it seems that the pmd is not present for the pages. If
>> someone has done investigation on this before please send me a reply.
>>
> Kernel linear memory isn't necessarily mapped by the page tables.  
> What are you trying to do and with what processor ?
>
>
>
> Ben.
>
>
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