Messages in this thread |  | | Date | Thu, 27 Sep 2001 15:00:31 +0200 (CEST) | From | Ingo Molnar <> | Subject | Re: __get_free_pages(): is the MEM really mine? |
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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
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