addresses returned by __get_free_pages()

addresses returned by __get_free_pages()

[Martin Maletinsky]

Hello,

In the 2.4.x kernel, can I apply the virt_to_page() macro to any address allocated by __get_free_pages() (i.e. when calling ret = __get_free_pages(flags, order), to any
address in the interval [retval,  2^order * PAGE_SIZE])?

In other words are those addresses guaranteed to be kernel logical addresses (i.e. between PAGE_OFFSET and PAGE_OFFSET + high_memory (on ix86))?

I know that in the 2.2.x kernel this used to be the case (i.e. __get_free_pages() returned kernel
logical addresses, to which virt_to_page() could be applied), but I don't quite understand the
memory managment of 2.4.x yet.

Thanks in advance for any help
regards
Martin


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Re: addresses returned by __get_free_pages()

[Stephen C. Tweedie]

Hi,

On Fri, Feb 08, 2002 at 10:21:33AM +0100, Martin Maletinsky wrote:
 
> In the 2.4.x kernel, can I apply the virt_to_page() macro to any address allocated by __get_free_pages() (i.e. when calling ret = __get_free_pages(flags, order), to any
> address in the interval [retval,  2^order * PAGE_SIZE])?

Yes, but it's easier just to call "alloc_pages(flags, order)", which
returns a struct page in the first place.

> In other words are those addresses guaranteed to be kernel logical addresses (i.e. between PAGE_OFFSET and PAGE_OFFSET + high_memory (on ix86))?

Yes, unless you specify GFP_HIGHMEM in the allocation flags.

Cheers,
 Stephen
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