Re: Implications of PG_locked and reference count in page structures....

[Daniel Phillips <phillips@bonn-fries.net>]

On August 15, 2001 05:39 pm, Michael Heinz wrote:
> I'm in the process of porting a driver to Linux. The author of the 
> driver conveniently broke it into os-dependent and independent sections.
> 
> One of the things in the "OS" dependent section is a routine to lock a 
> section of memory presumably to be used for DMA.
> 
> So, what I want to do is this: given a pointer to a previously 
> kmalloc'ed block, and the length of that block, I want to (a) identify 
> each page associated with the block and (b) lock each page. It appears 
> that I can lock the page either by incrementing it's reference count, or 
> by setting the PG_locked flag for the page.
> 
> Which method is preferred? Is there another method I should be using 
> instead?

See the other replies - you do not need to memlock your pages because you
will be allocating non-pageable kernel memory.

But for future reference, PG_locked is for serializing IO/cache
operations.  You use the page reference count to prevent a page from
being freed, i.e., to memlock it.  You'll see such object ref-counting
schemes showing up all through the kernel in slight variations.

--
Daniel