linux-kernel - Re: [PATCH 2/5] hugetlb: add phys addr to struct huge_bootmem

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Message-Id: <786B027A-4EC8-4175-A18D-9DA57E9549D6@kernel.crashing.org>
Date:	Thu, 30 Jun 2011 13:50:24 -0500
From:	Becky Bruce <beckyb@...nel.crashing.org>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	"List linux-kernel@...r.kernel.org Mailing" 
	<linux-kernel@...r.kernel.org>, linuxppc-dev@...ts.ozlabs.org,
	David Gibson <david@...son.dropbear.id.au>,
	Kumar Gala <galak@...nel.crashing.org>
Subject: Re: [PATCH 2/5] hugetlb: add phys addr to struct huge_bootmem_page


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

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