how can I cleanly exclude memory from the kernel memory allocator?

Larry Bassel lbassel at
Wed Apr 20 15:22:47 EDT 2011

On 19 Apr 11 23:48, Colin Cross wrote:
> On Tue, Apr 19, 2011 at 4:33 PM, Larry Bassel <lbassel at> wrote:
> > On 25 Mar 11 20:27, Russell King - ARM Linux wrote:
> >> On Fri, Mar 25, 2011 at 10:39:28AM -0700, Larry Bassel wrote:
> >> > OK, please ignore my previous mail, I see that .fixup can be
> >> > used to adjust tags. It appears to me, however, that using a
> >> > .reserve function calling memblock_reserve will be an
> >> > easier way of doing what I need.
> >>
> >> Absolutely.
> >
> > Hopefully I'm just missing something obvious, but
> > when I call memblock_reserve (in .38) to reserve a block
> > of memory away from the general kernel memory pool,
> > I find that an ioremap of memory within the reserved block
> > still fails because pte_valid() is apparently true.
> >
> > Is this intended behavior? If so, what would the
> > correct way of separating memory from the system be
> > so that there is no longer a 1-to-1 1M mapping for
> > this memory and ioremap (creating the *only* mapping
> > for this memory) is allowed?
> You need to call memblock_remove, not memblock_reserve.

Yes, that works for our platforms which don't use SPARSEMEM. Thanks.

Unfortunately, in the SPARSEMEM case pfn_valid() appears
(include/linux/mmzone.h) to only check if the section the
page frame is in has SECTION_HAS_MEM_MAP set, which memblock_removing
a part of a section doesn't (and presumably shouldn't) unset, so
pfn_valid() is still true for such pages.


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