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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 182 insertions, 1 deletions

diff --git a/arch/sparc/mm/Makefile b/arch/sparc/mm/Makefile
index 79836a7dd00c..e3cda21b5ee9 100644
--- a/arch/sparc/mm/Makefile
+++ b/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
diff --git a/arch/sparc/mm/gup.c b/arch/sparc/mm/gup.c
new file mode 100644
index 000000000000..a986b5d05712
--- /dev/null
+++ b/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;
+        }
+}