Messages in this thread |  | | Date | Sun, 30 Sep 2001 14:59:01 +0200 | From | Bernd Harries <> | Subject | Re: __get_free_pages(): is the MEM really mine? |
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Ingo Molnar wrote:
> This is a property of Linux's buddy allocator. If you allocate a 9th order > 'big page', that does not mean you can free the pages one by one.
I used free_pages((ULONG)card_ptr->dma_blk0[n], max_order); before Roman changed it. And still do for minor 26 now...
> while unconventional, doing this is safe. There is nothing in the page > structure that says that the page was allocated as a higher order page.
> But the above is an 'internal' property of > the Linux page allocator, so it's not guaranteed to stay so forever.
Thats why I don't like it so much. But it seems I must do it for some strange reason:
On minor 26 I do it the old way, on minor 27 I use Romans fix. What shall I say: Reading and writing to the buffer allocated with Roman's fix so far never crashed the system. But doing it the normal way (minor 26) how I also learned it from A. Rubini's book, does harm to the system.
After usage of the normally allocated buffer the strangest thing occur: - Issing w caused a dump on the console once. - Halt doesn't really halt the system completely - Reboot caused everything to hang, partitions still dirty...
> (the Linux kernel does not do the above for understandable reasons: it > takes a loop of 512 iterations to fix up the page counts in the above way, > which is noticeable runtime overhead.)
Oh yes, indeed! But:
Is there a guarantee that the n - 1 pages above the 1st one are not donated to other programs while my driver uses them?
> is it a fundamental property of the hardware that it needs a continuous > physical memory buffer?
Yes. The FW on the card demands it.
> Being able to allocate a 2 MB page is only guaranteed during bootup. There > is just no mechanizm in Linux that guarantees it for you to be able to > allocate a 2 MB page (let alone two adjacent 2 MB pages), in even a > moderately utilized system. Scatter-gather avoids all these problems.
I'll move the code to init_module later once it is stable.
Ciao, -- Bernd Harries
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