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    Subject[PATCH 4/4] sparc64: Implement get_user_pages_fast().
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Link: http://lkml.kernel.org/r/20100408.180015.30977694.davem@davemloft.net
    ---
    arch/sparc/mm/Makefile | 2
    arch/sparc/mm/gup.c | 181 +++++++++++++++++++++++++++++++++++++++++++++++++
    2 files changed, 182 insertions(+), 1 deletion(-)
    create mode 100644 arch/sparc/mm/gup.c

    Index: linux-2.6/arch/sparc/mm/Makefile
    ===================================================================
    --- linux-2.6.orig/arch/sparc/mm/Makefile
    +++ linux-2.6/arch/sparc/mm/Makefile
    @@ -4,7 +4,7 @@
    asflags-y := -ansi
    ccflags-y := -Werror

    -obj-$(CONFIG_SPARC64) += ultra.o tlb.o tsb.o
    +obj-$(CONFIG_SPARC64) += ultra.o tlb.o tsb.o gup.o
    obj-y += fault_$(BITS).o
    obj-y += init_$(BITS).o
    obj-$(CONFIG_SPARC32) += loadmmu.o
    Index: linux-2.6/arch/sparc/mm/gup.c
    ===================================================================
    --- /dev/null
    +++ linux-2.6/arch/sparc/mm/gup.c
    @@ -0,0 +1,181 @@
    +/*
    + * Lockless get_user_pages_fast for sparc, cribbed from powerpc
    + *
    + * Copyright (C) 2008 Nick Piggin
    + * Copyright (C) 2008 Novell Inc.
    + */
    +
    +#include <linux/sched.h>
    +#include <linux/mm.h>
    +#include <linux/vmstat.h>
    +#include <linux/pagemap.h>
    +#include <linux/rwsem.h>
    +#include <asm/pgtable.h>
    +
    +/*
    + * The performance critical leaf functions are made noinline otherwise gcc
    + * inlines everything into a single function which results in too much
    + * register pressure.
    + */
    +static noinline int gup_pte_range(pmd_t pmd, unsigned long addr,
    + unsigned long end, int write, struct page **pages, int *nr)
    +{
    + unsigned long mask, result;
    + pte_t *ptep;
    +
    + if (tlb_type == hypervisor) {
    + result = _PAGE_PRESENT_4V|_PAGE_P_4V;
    + if (write)
    + result |= _PAGE_WRITE_4V;
    + } else {
    + result = _PAGE_PRESENT_4U|_PAGE_P_4U;
    + if (write)
    + result |= _PAGE_WRITE_4U;
    + }
    + mask = result | _PAGE_SPECIAL;
    +
    + ptep = pte_offset_kernel(&pmd, addr);
    + do {
    + struct page *page, *head;
    + pte_t pte = *ptep;
    +
    + if ((pte_val(pte) & mask) != result)
    + return 0;
    + VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
    +
    + /* The hugepage case is simplified on sparc64 because
    + * we encode the sub-page pfn offsets into the
    + * hugepage PTEs. We could optimize this in the future
    + * use page_cache_add_speculative() for the hugepage case.
    + */
    + page = pte_page(pte);
    + head = compound_head(page);
    + if (!page_cache_get_speculative(head))
    + return 0;
    + if (unlikely(pte_val(pte) != pte_val(*ptep))) {
    + put_page(head);
    + return 0;
    + }
    +
    + pages[*nr] = page;
    + (*nr)++;
    + } while (ptep++, addr += PAGE_SIZE, addr != end);
    +
    + return 1;
    +}
    +
    +static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
    + int write, struct page **pages, int *nr)
    +{
    + unsigned long next;
    + pmd_t *pmdp;
    +
    + pmdp = pmd_offset(&pud, addr);
    + do {
    + pmd_t pmd = *pmdp;
    +
    + next = pmd_addr_end(addr, end);
    + if (pmd_none(pmd))
    + return 0;
    + if (!gup_pte_range(pmd, addr, next, write, pages, nr))
    + return 0;
    + } while (pmdp++, addr = next, addr != end);
    +
    + return 1;
    +}
    +
    +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(&pgd, addr);
    + do {
    + pud_t pud = *pudp;
    +
    + next = pud_addr_end(addr, end);
    + if (pud_none(pud))
    + return 0;
    + if (!gup_pmd_range(pud, addr, next, write, pages, nr))
    + return 0;
    + } while (pudp++, addr = next, addr != end);
    +
    + return 1;
    +}
    +
    +int get_user_pages_fast(unsigned long start, int nr_pages, int write,
    + struct page **pages)
    +{
    + struct mm_struct *mm = current->mm;
    + unsigned long addr, len, end;
    + unsigned long next;
    + pgd_t *pgdp;
    + int nr = 0;
    +
    + start &= PAGE_MASK;
    + addr = start;
    + len = (unsigned long) nr_pages << PAGE_SHIFT;
    + end = start + len;
    +
    + /*
    + * XXX: batch / limit 'nr', to avoid large irq off latency
    + * needs some instrumenting to determine the common sizes used by
    + * important workloads (eg. DB2), and whether limiting the batch size
    + * will decrease performance.
    + *
    + * It seems like we're in the clear for the moment. Direct-IO is
    + * the main guy that batches up lots of get_user_pages, and even
    + * they are limited to 64-at-a-time which is not so many.
    + */
    + /*
    + * This doesn't prevent pagetable teardown, but does prevent
    + * the pagetables from being freed on sparc.
    + *
    + * So long as we atomically load page table pointers versus teardown,
    + * we can follow the address down to the the page and take a ref on it.
    + */
    + local_irq_disable();
    +
    + pgdp = pgd_offset(mm, addr);
    + do {
    + pgd_t pgd = *pgdp;
    +
    + next = pgd_addr_end(addr, end);
    + if (pgd_none(pgd))
    + goto slow;
    + if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
    + goto slow;
    + } while (pgdp++, addr = next, addr != end);
    +
    + local_irq_enable();
    +
    + VM_BUG_ON(nr != (end - start) >> PAGE_SHIFT);
    + return nr;
    +
    + {
    + int ret;
    +
    +slow:
    + local_irq_enable();
    +
    + /* Try to get the remaining pages with get_user_pages */
    + start += nr << PAGE_SHIFT;
    + pages += nr;
    +
    + down_read(&mm->mmap_sem);
    + ret = get_user_pages(current, mm, start,
    + (end - start) >> PAGE_SHIFT, write, 0, pages, NULL);
    + up_read(&mm->mmap_sem);
    +
    + /* Have to be a bit careful with return values */
    + if (nr > 0) {
    + if (ret < 0)
    + ret = nr;
    + else
    + ret += nr;
    + }
    +
    + return ret;
    + }
    +}



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