Re: [RFC][patch 0/2] mm: remove PageReserved

Martin J. Bligh
2005-08-09T14:38:52Z

--Russell King <rmk+lkml@arm.linux.org.uk> wrote (on Tuesday, August 09, 2005 08:08:53 +0100):

> On Tue, Aug 09, 2005 at 02:59:53PM +1000, Nick Piggin wrote:
>> That would work for swsusp, but there are other users that want to
>> know if a struct page is valid ram (eg. ioremap), so in that case
>> swsusp would not be able to mess with the flag.
>
> The usage of "valid ram" here is confusing - that's not what PageReserved
> is all about. It's about valid RAM which is managed by method other
> than the usual page counting. Non-reserved RAM is also valid RAM, but
> is managed by the kernel in the usual way.
>
> The former is available for remap_pfn_range and ioremap, the latter is
> not.
>
> On the other hand, the validity of an apparant RAM address can only be
> tested using its pfn with pfn_valid().
>
> Can we straighten out the terminology so it's less confusing please?

pfn_valid() doesn't tell you it's RAM or not - it tells you whether you
have a backing struct page for that address. Could be an IO mapped device,
a small memory hole, whatever.

M.