Patchwork [2/5] hugetlb: add phys addr to struct huge_bootmem_page

From: Becky Bruce <beckyb@kernel.crashing.org>

This is needed on HIGHMEM systems - we don't always have a virtual
address so store the physical address and map it in as needed.

Signed-off-by: Becky Bruce <beckyb@kernel.crashing.org>
---
 include/linux/hugetlb.h |    3 +++
 mm/hugetlb.c            |    8 +++++++-
 2 files changed, 10 insertions(+), 1 deletions(-)

On Tue, 2011-06-28 at 14:54 -0500, Becky Bruce wrote:
>  struct page *alloc_huge_page_node(struct hstate *h, int nid);
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 6402458..2db81ea 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1105,8 +1105,14 @@ static void __init
> gather_bootmem_prealloc(void)
>         struct huge_bootmem_page *m;
>  
>         list_for_each_entry(m, &huge_boot_pages, list) {
> -               struct page *page = virt_to_page(m);
>                 struct hstate *h = m->hstate;
> +#ifdef CONFIG_HIGHMEM
> +               struct page *page = pfn_to_page(m->phys >>
> PAGE_SHIFT);
> +               free_bootmem_late((unsigned long)m,
> +                                 sizeof(struct huge_bootmem_page));
> +#else
> +               struct page *page = virt_to_page(m);
> +#endif
>                 __ClearPageReserved(page);

Why do you add free_bootmem_late() in the highmem case and not the
normal case ?

Cheers,
Ben.

On Jun 28, 2011, at 4:39 PM, Benjamin Herrenschmidt wrote:

> On Tue, 2011-06-28 at 14:54 -0500, Becky Bruce wrote:
>> struct page *alloc_huge_page_node(struct hstate *h, int nid);
>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>> index 6402458..2db81ea 100644
>> --- a/mm/hugetlb.c
>> +++ b/mm/hugetlb.c
>> @@ -1105,8 +1105,14 @@ static void __init
>> gather_bootmem_prealloc(void)
>>        struct huge_bootmem_page *m;
>> 
>>        list_for_each_entry(m, &huge_boot_pages, list) {
>> -               struct page *page = virt_to_page(m);
>>                struct hstate *h = m->hstate;
>> +#ifdef CONFIG_HIGHMEM
>> +               struct page *page = pfn_to_page(m->phys >>
>> PAGE_SHIFT);
>> +               free_bootmem_late((unsigned long)m,
>> +                                 sizeof(struct huge_bootmem_page));
>> +#else
>> +               struct page *page = virt_to_page(m);
>> +#endif
>>                __ClearPageReserved(page);
> 
> Why do you add free_bootmem_late() in the highmem case and not the
> normal case ?

Because there was no bootmem allocation in the normal case - the non-highmem version stores data structure in the huge page itself.  This is perfectly fine as long as you have a mapping.  Since this isn't true for HIGHMEM pages, I allocate bootmem to store the early data structure that stores information about the hugepage (this happens in arch-specific code in alloc_bootmem_huge_page).

-Becky

On Thu, Jun 30, 2011 at 1:50 PM, Becky Bruce <beckyb@kernel.crashing.org> wrote:

> Because there was no bootmem allocation in the normal case - the non-highmem
> version stores data structure in the huge page itself.  This is perfectly fine as long
> as you have a mapping.  Since this isn't true for HIGHMEM pages, I allocate
> bootmem to store the early data structure that stores information about the
> hugepage (this happens in arch-specific code in alloc_bootmem_huge_page).

I would put this text in a comment in the code.