Re: [Libhugetlbfs-devel] Buglet in 16G page handling

Jon Tollefson
2008-09-03T22:19:14Z

David Gibson wrote:
> On Tue, Sep 02, 2008 at 12:12:27PM -0500, Jon Tollefson wrote:
>
>> David Gibson wrote:
>>
>>> When BenH and I were looking at the new code for handling 16G pages,
>>> we noticed a small bug. It doesn't actually break anything user
>>> visible, but it's certainly not the way things are supposed to be.
>>> The 16G patches didn't update the huge_pte_offset() and
>>> huge_pte_alloc() functions, which means that the hugepte tables for
>>> 16G pages will be allocated much further down the page table tree than
>>> they should be - allocating several levels of page table with a single
>>> entry in them along the way.
>>>
>>> The patch below is supposed to fix this, cleaning up the existing
>>> handling of 64k vs 16M pages while its at it. However, it needs some
>>> testing.
>>>
>>> I've checked that it doesn't break existing 16M support, either with
>>> 4k or 64k base pages. I haven't figured out how to test with 64k
>>> pages yet, at least until the multisize support goes into
>>> libhugetlbfs. For 16G pages, I just don't have access to a machine
>>> with enough memory to test. Jon, presumably you must have found such
>>> a machine when you did the 16G page support in the first place. Do
>>> you still have access, and can you test this patch?
>>>
>>>
>> I do have access to a machine to test it. I applied the patch to -rc4
>> and used a pseries_defconfig. I boot with
>> default_hugepagesz=16G... in order to test huge page sizes other then
>> 16M at this point.
>>
>> Running the libhugetlbfs test suite it gets as far as Readback (64):
>> PASS
>> before it hits the following program check.
>>
>
> Ah, yes, oops, forgot to fix up the pagetable freeing path in line
> with the other changes. Try the revised version below.
>
I have run through the tests twice now with this new patch using a 4k
base page size(and 16G huge page size) and there are no program checks
or spin lock issues. So looking good.

I will run it next a couple of times with 64K base pages.

Jon

> Index: working-2.6/arch/powerpc/mm/hugetlbpage.c
> ===================================================================
> --- working-2.6.orig/arch/powerpc/mm/hugetlbpage.c 2008-09-02 11:50:12.000000000 +1000
> +++ working-2.6/arch/powerpc/mm/hugetlbpage.c 2008-09-03 10:10:54.000000000 +1000
> @@ -128,29 +128,37 @@ static int __hugepte_alloc(struct mm_str
> return 0;
> }
>
> -/* Base page size affects how we walk hugetlb page tables */
> -#ifdef CONFIG_PPC_64K_PAGES
> -#define hpmd_offset(pud, addr, h) pmd_offset(pud, addr)
> -#define hpmd_alloc(mm, pud, addr, h) pmd_alloc(mm, pud, addr)
> -#else
> -static inline
> -pmd_t *hpmd_offset(pud_t *pud, unsigned long addr, struct hstate *hstate)
> +
> +static pud_t *hpud_offset(pgd_t *pgd, unsigned long addr, struct hstate *hstate)
> +{
> + if (huge_page_shift(hstate) < PUD_SHIFT)
> + return pud_offset(pgd, addr);
> + else
> + return (pud_t *) pgd;
> +}
> +static pud_t *hpud_alloc(struct mm_struct *mm, pgd_t *pgd, unsigned long addr,
> + struct hstate *hstate)
> {
> - if (huge_page_shift(hstate) == PAGE_SHIFT_64K)
> + if (huge_page_shift(hstate) < PUD_SHIFT)
> + return pud_alloc(mm, pgd, addr);
> + else
> + return (pud_t *) pgd;
> +}
> +static pmd_t *hpmd_offset(pud_t *pud, unsigned long addr, struct hstate *hstate)
> +{
> + if (huge_page_shift(hstate) < PMD_SHIFT)
> return pmd_offset(pud, addr);
> else
> return (pmd_t *) pud;
> }
> -static inline
> -pmd_t *hpmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long addr,
> - struct hstate *hstate)
> +static pmd_t *hpmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long addr,
> + struct hstate *hstate)
> {
> - if (huge_page_shift(hstate) == PAGE_SHIFT_64K)
> + if (huge_page_shift(hstate) < PMD_SHIFT)
> return pmd_alloc(mm, pud, addr);
> else
> return (pmd_t *) pud;
> }
> -#endif
>
> /* Build list of addresses of gigantic pages. This function is used in early
> * boot before the buddy or bootmem allocator is setup.
> @@ -204,7 +212,7 @@ pte_t *huge_pte_offset(struct mm_struct
>
> pg = pgd_offset(mm, addr);
> if (!pgd_none(*pg)) {
> - pu = pud_offset(pg, addr);
> + pu = hpud_offset(pg, addr, hstate);
> if (!pud_none(*pu)) {
> pm = hpmd_offset(pu, addr, hstate);
> if (!pmd_none(*pm))
> @@ -233,7 +241,7 @@ pte_t *huge_pte_alloc(struct mm_struct *
> addr &= hstate->mask;
>
> pg = pgd_offset(mm, addr);
> - pu = pud_alloc(mm, pg, addr);
> + pu = hpud_alloc(mm, pg, addr, hstate);
>
> if (pu) {
> pm = hpmd_alloc(mm, pu, addr, hstate);
> @@ -316,13 +324,7 @@ static void hugetlb_free_pud_range(struc
> pud = pud_offset(pgd, addr);
> do {
> next = pud_addr_end(addr, end);
> -#ifdef CONFIG_PPC_64K_PAGES
> - if (pud_none_or_clear_bad(pud))
> - continue;
> - hugetlb_free_pmd_range(tlb, pud, addr, next, floor, ceiling,
> - psize);
> -#else
> - if (shift == PAGE_SHIFT_64K) {
> + if (shift < PMD_SHIFT) {
> if (pud_none_or_clear_bad(pud))
> continue;
> hugetlb_free_pmd_range(tlb, pud, addr, next, floor,
> @@ -332,7 +334,6 @@ static void hugetlb_free_pud_range(struc
> continue;
> free_hugepte_range(tlb, (hugepd_t *)pud, psize);
> }
> -#endif
> } while (pud++, addr = next, addr != end);
>
> start &= PGDIR_MASK;
> @@ -422,9 +423,15 @@ void hugetlb_free_pgd_range(struct mmu_g
> psize = get_slice_psize(tlb->mm, addr);
> BUG_ON(!mmu_huge_psizes[psize]);
> next = pgd_addr_end(addr, end);
> - if (pgd_none_or_clear_bad(pgd))
> - continue;
> - hugetlb_free_pud_range(tlb, pgd, addr, next, floor, ceiling);
> + if (mmu_psize_to_shift(psize) < PUD_SHIFT) {
> + if (pgd_none_or_clear_bad(pgd))
> + continue;
> + hugetlb_free_pud_range(tlb, pgd, addr, next, floor, ceiling);
> + } else {
> + if (pgd_none(*pgd))
> + continue;
> + free_hugepte_range(tlb, (hugepd_t *)pgd, psize);
> + }
> } while (pgd++, addr = next, addr != end);
> }
>
>
>
>