Re: [PATCH] Physical Memory Management [0/1]

Peter Zijlstra
2009-05-14T12:05:03Z

On Thu, 2009-05-14 at 13:48 +0200, MichaA? Nazarewicz wrote:
> > On Thu, 2009-05-14 at 11:00 +0200, MichaA? Nazarewicz wrote:
> >> PMM solves this problem since the buffers are allocated when they
> >> are needed.
>
> On Thu, 14 May 2009 13:20:02 +0200, Peter Zijlstra wrote:
> > Ha - only when you actually manage to allocate things. Physically
> > contiguous allocations are exceedingly hard once the machine has been
> > running for a while.
>
> PMM reserves memory during boot time using alloc_bootmem_low_pages().
> After this is done, it can allocate buffers from reserved pool.
>
> The idea here is that there are n hardware accelerators, each
> can operate on 1MiB blocks (to simplify assume that's the case).
> However, we know that at most m < n devices will be used at the same
> time so instead of reserving n MiBs of memory we reserve only m MiBs.

And who says your pre-allocated pool won't fragment with repeated PMM
use?