On Thu, 29 Dec 2005, Avishay Traeger wrote:
> How does the kernel determine when a page is unused? I see that
> __get_free_pages() returns pages that have no refcount and no flags
> indicating that they should not be reclaimed.
>
> The first page that is returned looks like:
> flags:0x80000000 mapping:00000000 mapcount:0 count:1
>
> And the subsequent pages look like:
> flags:0x80000000 mapping:00000000 mapcount:0 count:0
>
> I am printing this out exactly the way bad_page() does. How does the
> kernel know not to mess around with pages that have no refcount or any
> flags to indicate that they are in use? I've already searched google
> and checked a couple books, and couldn't find an answer.
The kernel knows that a page is free if count == 0 in the first page.
All pages of a higher order allocation are managed through the status of
the first page.
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