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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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