lkml.org 
[lkml]   [2001]   [Sep]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: __get_free_pages(): is the MEM really mine?

On Thu, 27 Sep 2001, Bernd Harries wrote:

> > have you perpahs freed that page?
>
> Yes, as expected.

well - what did you expect to happen? A freed page is going to be reused
for other purposes. A big 2MB allocation can be reused in part, once
memory usage grows. So you should not expect the device to be able to DMA
into a page that got freed, unpunished. Perhaps i'm misunderstanding the
problem.

> But I tend to conclude from getting the same phys address again after
> some time that noone else uses much memory inbetween. Plus, the first
> page of the area stays Zero all the time while the higher pages seem
> to be used by someone. [...]

the buddy allocator allocates top down. Plus, if you allocate a 2MB
physically continuous chunk then the likelyhood is high that there were
fragmented pages skipped during the initial search for a 2MB block - so
you still have a fair likelyhood to reallocate it after some time, if
memory usage is light. But this likelyhood nears zero once RAM usage gets
near 100%.

Ingo

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 13:03    [W:0.078 / U:2.332 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site