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Date: Tue, 18 Jul 2006 21:45:10 -0700 (PDT)
From: Parav Pandit <paravpandit@yahoo.com>
Subject: Re: page locking in PowerPC cores
To: Eugene Surovegin <ebs@ebshome.net>
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--- Eugene Surovegin <ebs@ebshome.net> wrote:
> >   We allocate memory for DMA operation on PCI
> device using pci_alloc_constistent().
> >    
> >   I want to know how this function is boil down to
> the actual instruction which locks the page in the
> RAM so that it cannot be paged out and dma can do
> its work.
> 
> This is trivial - you can start with looking at the
> implementation.
> 

[Parav]
I did it, but after reaching __alloc_pages() its
getting difficult to understand.
Here is the sequence:
pci_alloc_consistent()
-> __get_free_pages()
   ->alloc_pages(gfp_mask, order)
      ->alloc_pages_current()
         -> __alloc_pages()

It does something with zones. Looks like zone memory
pages are locked in the beginning.
Still could not figure out the instuctions for page
locking.


> >    
> >   Can anybody tell me which instructions do we use
> to set this page entry in TLB and page table?
> >   What bit gets set in the PTE for this?
> 
> Why do you need this page in TLB?

[Parav] No, I don't want. I just wanted to see the
code for locking inside TLB or in page table.


> 
> In general you don't have to worry about _any_
> memory you allocated in 
> the kernel to be paged out.
> 

[Parav] As driver writer, I agree I don't need to, but
to better understand the system I am eager to do that.

Regards,
Parav


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