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Message-ID: <20141028104129.GA4187@linaro.org>
Date: Tue, 28 Oct 2014 10:41:31 +0000
From: Steve Capper <steve.capper@...aro.org>
To: "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc: akpm@...ux-foundation.org, Andrea Arcangeli <aarcange@...hat.com>,
benh@...nel.crashing.org, mpe@...erman.id.au, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
linux-arch@...r.kernel.org
Subject: Re: [PATCH V3 1/2] mm: Update generic gup implementation to handle
hugepage directory
On Sat, Oct 25, 2014 at 04:14:19PM +0530, Aneesh Kumar K.V wrote:
> Update generic gup implementation with powerpc specific details.
> On powerpc at pmd level we can have hugepte, normal pmd pointer
> or a pointer to the hugepage directory.
>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
> ---
Hi,
Apologies for not getting to this yesterday.
I have some comments below:
> Changes from V3:
> * Explain pgd_huge, also move the definition to linux/hugetlb.h.
> Both pgd_huge and is_hugepd are related to hugepages and hugetlb.h
> is the right header
>
> arch/arm/include/asm/pgtable.h | 2 +
> arch/arm64/include/asm/pgtable.h | 2 +
> arch/powerpc/include/asm/page.h | 1 +
> include/linux/hugetlb.h | 30 +++++++++++
> include/linux/mm.h | 7 +++
> mm/gup.c | 113 +++++++++++++++++++--------------------
> 6 files changed, 96 insertions(+), 59 deletions(-)
>
> diff --git a/arch/arm/include/asm/pgtable.h b/arch/arm/include/asm/pgtable.h
> index 3b30062..c52d261 100644
> --- a/arch/arm/include/asm/pgtable.h
> +++ b/arch/arm/include/asm/pgtable.h
> @@ -181,6 +181,8 @@ extern pgd_t swapper_pg_dir[PTRS_PER_PGD];
> /* to find an entry in a kernel page-table-directory */
> #define pgd_offset_k(addr) pgd_offset(&init_mm, addr)
>
> +#define pgd_huge(pgd) (0)
> +
Please remove this from the patch as it is no longer needed due to
some changes below.
> #define pmd_none(pmd) (!pmd_val(pmd))
> #define pmd_present(pmd) (pmd_val(pmd))
>
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index 41a43bf..f532a14 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -464,6 +464,8 @@ static inline pmd_t pmd_modify(pmd_t pmd, pgprot_t newprot)
> extern pgd_t swapper_pg_dir[PTRS_PER_PGD];
> extern pgd_t idmap_pg_dir[PTRS_PER_PGD];
>
> +#define pgd_huge(pgd) (0)
> +
This too can be removed (see below)...
> /*
> * Encode and decode a swap entry:
> * bits 0-1: present (must be zero)
> diff --git a/arch/powerpc/include/asm/page.h b/arch/powerpc/include/asm/page.h
> index 26fe1ae..f973fce 100644
> --- a/arch/powerpc/include/asm/page.h
> +++ b/arch/powerpc/include/asm/page.h
> @@ -380,6 +380,7 @@ static inline int hugepd_ok(hugepd_t hpd)
> #endif
>
> #define is_hugepd(pdep) (hugepd_ok(*((hugepd_t *)(pdep))))
> +#define pgd_huge pgd_huge
> int pgd_huge(pgd_t pgd);
> #else /* CONFIG_HUGETLB_PAGE */
> #define is_hugepd(pdep) 0
> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index 6e6d338..de63dbc 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -175,6 +175,36 @@ static inline void __unmap_hugepage_range(struct mmu_gather *tlb,
> }
>
> #endif /* !CONFIG_HUGETLB_PAGE */
> +/*
> + * hugepages at page global directory. If arch support
> + * hugepages at pgd level, they need to define this.
> + */
> +#ifndef pgd_huge
> +#define pgd_huge(x) 0
> +#endif
This sequence now means we no longer need per-arch non-trivial
definitions of pgd_huge. i.e. it makes the arch/arm and arch/arm64
changes above superfluous.
> +
> +#ifndef is_hugepd
> +/*
> + * Some architectures requires a hugepage directory format that is
> + * required to support multiple hugepage sizes. For example
> + * a4fe3ce7699bfe1bd88f816b55d42d8fe1dac655 introduced the same
> + * on powerpc. This allows for a more flexible hugepage pagetable
> + * layout.
> + */
> +typedef struct { unsigned long pd; } hugepd_t;
> +#define is_hugepd(hugepd) (0)
> +#define __hugepd(x) ((hugepd_t) { (x) })
> +static inline int gup_huge_pd(hugepd_t hugepd, unsigned long addr,
> + unsigned pdshift, unsigned long end,
> + int write, struct page **pages, int *nr)
> +{
> + return 0;
> +}
> +#else
> +extern int gup_huge_pd(hugepd_t hugepd, unsigned long addr,
> + unsigned pdshift, unsigned long end,
> + int write, struct page **pages, int *nr);
> +#endif
>
> #define HUGETLB_ANON_FILE "anon_hugepage"
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 02d11ee..31d7fac 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1219,6 +1219,13 @@ long get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
> struct vm_area_struct **vmas);
> int get_user_pages_fast(unsigned long start, int nr_pages, int write,
> struct page **pages);
> +
> +#ifdef CONFIG_HAVE_GENERIC_RCU_GUP
> +extern int gup_huge_pte(pte_t orig, pte_t *ptep, unsigned long addr,
> + unsigned long sz, unsigned long end, int write,
> + struct page **pages, int *nr);
> +#endif
> +
> struct kvec;
> int get_kernel_pages(const struct kvec *iov, int nr_pages, int write,
> struct page **pages);
> diff --git a/mm/gup.c b/mm/gup.c
> index cd62c8c..30773f3 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -786,65 +786,31 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
> }
> #endif /* __HAVE_ARCH_PTE_SPECIAL */
>
> -static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
> - unsigned long end, int write, struct page **pages, int *nr)
> +int gup_huge_pte(pte_t orig, pte_t *ptep, unsigned long addr,
> + unsigned long sz, unsigned long end, int write,
> + struct page **pages, int *nr)
> {
> - struct page *head, *page, *tail;
> int refs;
> + unsigned long pte_end;
> + struct page *head, *page, *tail;
>
> - if (write && !pmd_write(orig))
> - return 0;
> -
> - refs = 0;
> - head = pmd_page(orig);
> - page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
> - tail = page;
> - do {
> - VM_BUG_ON_PAGE(compound_head(page) != head, page);
> - pages[*nr] = page;
> - (*nr)++;
> - page++;
> - refs++;
> - } while (addr += PAGE_SIZE, addr != end);
>
> - if (!page_cache_add_speculative(head, refs)) {
> - *nr -= refs;
> + if (write && !pte_write(orig))
> return 0;
> - }
>
> - if (unlikely(pmd_val(orig) != pmd_val(*pmdp))) {
> - *nr -= refs;
> - while (refs--)
> - put_page(head);
> + if (!pte_present(orig))
> return 0;
> - }
>
> - /*
> - * Any tail pages need their mapcount reference taken before we
> - * return. (This allows the THP code to bump their ref count when
> - * they are split into base pages).
> - */
> - while (refs--) {
> - if (PageTail(tail))
> - get_huge_page_tail(tail);
> - tail++;
> - }
> -
> - return 1;
> -}
> -
> -static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
> - unsigned long end, int write, struct page **pages, int *nr)
> -{
> - struct page *head, *page, *tail;
> - int refs;
> + pte_end = (addr + sz) & ~(sz-1);
> + if (pte_end < end)
> + end = pte_end;
>
> - if (write && !pud_write(orig))
> - return 0;
> + /* hugepages are never "special" */
> + VM_BUG_ON(!pfn_valid(pte_pfn(orig)));
>
> refs = 0;
> - head = pud_page(orig);
> - page = head + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
> + head = pte_page(orig);
> + page = head + ((addr & (sz-1)) >> PAGE_SHIFT);
> tail = page;
> do {
> VM_BUG_ON_PAGE(compound_head(page) != head, page);
> @@ -859,13 +825,18 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
> return 0;
> }
>
> - if (unlikely(pud_val(orig) != pud_val(*pudp))) {
> + if (unlikely(pte_val(orig) != pte_val(*ptep))) {
> *nr -= refs;
> while (refs--)
> put_page(head);
> return 0;
> }
>
> + /*
> + * Any tail pages need their mapcount reference taken before we
> + * return. (This allows the THP code to bump their ref count when
> + * they are split into base pages).
> + */
> while (refs--) {
> if (PageTail(tail))
> get_huge_page_tail(tail);
> @@ -898,10 +869,19 @@ static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
> if (pmd_numa(pmd))
> return 0;
>
> - if (!gup_huge_pmd(pmd, pmdp, addr, next, write,
> - pages, nr))
> + if (!gup_huge_pte(__pte(pmd_val(pmd)), (pte_t *)pmdp,
> + addr, PMD_SIZE, next,
> + write, pages, nr))
> return 0;
>
> + } else if (unlikely(is_hugepd(__hugepd(pmd_val(pmd))))) {
> + /*
> + * architecture have different format for hugetlbfs
> + * pmd format and THP pmd format
> + */
> + if (!gup_huge_pd(__hugepd(pmd_val(pmd)), addr,
> + PMD_SHIFT, next, write, pages, nr))
> + return 0;
> } else if (!gup_pte_range(pmd, addr, next, write, pages, nr))
> return 0;
> } while (pmdp++, addr = next, addr != end);
> @@ -909,22 +889,27 @@ static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
> return 1;
> }
The new definition of gup_huge_pte does get rid of a lot of code
duplication, but it also introduces the assumption that HugeTLB pages
and THPs can have their attributes referenced by pte_ accessors (rather
than something like pmd_write for instance). Please add this assumption
to the list in the file above.
This will probably be important for pte_pfn and pte_page in case an
architecture packs more attribute bits into what would normally be the
lower address bits of a pte. (for arm and arm64 these bits are
currently unused and expected to be zero so this code works).
>
> -static int gup_pud_range(pgd_t *pgdp, unsigned long addr, unsigned long end,
> +static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long end,
> int write, struct page **pages, int *nr)
> {
> unsigned long next;
> pud_t *pudp;
>
> - pudp = pud_offset(pgdp, addr);
> + pudp = pud_offset(&pgd, addr);
> do {
> pud_t pud = ACCESS_ONCE(*pudp);
>
> next = pud_addr_end(addr, end);
> if (pud_none(pud))
> return 0;
> - if (pud_huge(pud)) {
> - if (!gup_huge_pud(pud, pudp, addr, next, write,
> - pages, nr))
> + if (unlikely(pud_huge(pud))) {
> + if (!gup_huge_pte(__pte(pud_val(pud)), (pte_t *)pudp,
> + addr, PUD_SIZE, next,
> + write, pages, nr))
> + return 0;
> + } else if (unlikely(is_hugepd(__hugepd(pud_val(pud))))) {
> + if (!gup_huge_pd(__hugepd(pud_val(pud)), addr,
> + PUD_SHIFT, next, write, pages, nr))
> return 0;
> } else if (!gup_pmd_range(pud, addr, next, write, pages, nr))
> return 0;
> @@ -970,10 +955,21 @@ int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
> local_irq_save(flags);
> pgdp = pgd_offset(mm, addr);
> do {
> + pgd_t pgd = ACCESS_ONCE(*pgdp);
> +
> next = pgd_addr_end(addr, end);
> - if (pgd_none(*pgdp))
> + if (pgd_none(pgd))
> break;
> - else if (!gup_pud_range(pgdp, addr, next, write, pages, &nr))
> + if (unlikely(pgd_huge(pgd))) {
> + if (!gup_huge_pte(__pte(pgd_val(pgd)), (pte_t *)pgdp,
> + addr, PGDIR_SIZE, next,
> + write, pages, &nr))
> + break;
> + } else if (unlikely(is_hugepd(__hugepd(pgd_val(pgd))))) {
> + if (!gup_huge_pd(__hugepd(pgd_val(pgd)), addr,
> + PGDIR_SHIFT, next, write, pages, &nr))
> + break;
> + } else if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
> break;
> } while (pgdp++, addr = next, addr != end);
> local_irq_restore(flags);
> @@ -1028,5 +1024,4 @@ int get_user_pages_fast(unsigned long start, int nr_pages, int write,
>
> return ret;
> }
> -
> #endif /* CONFIG_HAVE_GENERIC_RCU_GUP */
> --
With the above changes (remove the arch/arm and arch/arm64 changes and
add an extra assumption to the list for gup_huge_pte):
Acked-by: Steve Capper <steve.capper@...aro.org>
Also, I've tested this on an Arndale board (arm) and a Juno board
(arm64); running a custom futex on THP tail test.
Cheers,
--
Steve
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