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SubjectRe: DMA page allocation
On Thu, 17 Jun 1999, Andrea Arcangeli wrote:

> On Wed, 16 Jun 1999, Jaroslav Kysela wrote:
>
> > I'm really tired with the chronic problem of the linux kernel:
> >DMA page allocation when the system memory size is far beyond 16MB.
>
> Could try if a simple:
>
> echo 255 510 765 >/proc/sys/vm/freepages
>
> will help low memory machines? You can also set these limits by hand

My solution wasn't intended to solve a problem with non-continuous memory
regions for low memory machines. I need to solve the problem for machines
with 16MB+ memory. I have big trouble with my 128MB machine - there is not
often free any DMA page.

> inside your driver that needs DMA memory often by using the sysctl syscall
> inside the kernel (or exporting the freepages symbols to modules 8)).
>
> You will waste some more base memory but I think you may get a far better
> behaviour.
>
> I never gone into the fragment issue so far but I have some idea about
> that, at first we should tell try_to_free_pages() which kild of memory
> order we are interested about. Then we should elaborate shrink_mmap and
> swap_out to work on `gfp_order' basis.

Could you say me what's wrong with my solution (two independent page
pools)? There are some things to discuss: When the system have up to 16MB
memory, the system should use only one pool for pages (on other side, it
may be good to have reserved some DMA pages). The size of the DMA memory
pool should be configurable.

I think that my solution give us better results than your with
try_to_free_pages() fiddling, because there will be always possibility to
have some pages locked for some reason when they are mixed one another,
thus they can't be freed.

Jaroslav

-----
Jaroslav Kysela <perex@suse.cz>
SuSE Linux http://www.suse.com
ALSA project http://www.alsa-project.org


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