The patch titled
powerpc: lockless get_user_pages
has been added to the -mm tree. Its filename is
powerpc-lockless-get_user_pages.patch
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See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
Subject: powerpc: lockless get_user_pages
From: Nick Piggin <npiggin@xxxxxxx>
Implement lockless get_user_pages_fast for powerpc. Page table existence
is guaranteed with RCU, and speculative page references are used to take a
reference to the pages without having a prior existence guarantee on them.
Signed-off-by: Nick Piggin <npiggin@xxxxxxx>
Signed-off-by: Dave Kleikamp <shaggy@xxxxxxxxxxxxxxxxxx>
Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Cc: Hugh Dickins <hugh@xxxxxxxxxxx>
Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
arch/powerpc/Kconfig | 3
arch/powerpc/mm/Makefile | 2
arch/powerpc/mm/gup.c | 258 ++++++++++++++++++++++++++
include/asm-powerpc/pgtable-ppc64.h | 2
include/linux/pagemap.h | 23 ++
5 files changed, 287 insertions(+), 1 deletion(-)
diff -puN arch/powerpc/Kconfig~powerpc-lockless-get_user_pages arch/powerpc/Kconfig
--- a/arch/powerpc/Kconfig~powerpc-lockless-get_user_pages
+++ a/arch/powerpc/Kconfig
@@ -42,6 +42,9 @@ config GENERIC_HARDIRQS
bool
default y
+config HAVE_GET_USER_PAGES_FAST
+ def_bool PPC64
+
config HAVE_SETUP_PER_CPU_AREA
def_bool PPC64
diff -puN arch/powerpc/mm/Makefile~powerpc-lockless-get_user_pages arch/powerpc/mm/Makefile
--- a/arch/powerpc/mm/Makefile~powerpc-lockless-get_user_pages
+++ a/arch/powerpc/mm/Makefile
@@ -6,7 +6,7 @@ ifeq ($(CONFIG_PPC64),y)
EXTRA_CFLAGS += -mno-minimal-toc
endif
-obj-y := fault.o mem.o \
+obj-y := fault.o mem.o gup.o \
init_$(CONFIG_WORD_SIZE).o \
pgtable_$(CONFIG_WORD_SIZE).o \
mmu_context_$(CONFIG_WORD_SIZE).o
diff -puN /dev/null arch/powerpc/mm/gup.c
--- /dev/null
+++ a/arch/powerpc/mm/gup.c
@@ -0,0 +1,258 @@
+/*
+ * Lockless get_user_pages_fast for powerpc
+ *
+ * Copyright (C) 2008 Nick Piggin
+ * Copyright (C) 2008 Novell Inc.
+ */
+#include <linux/sched.h>
+#include <linux/mm.h>
+#include <linux/hugetlb.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;
+
+ result = _PAGE_PRESENT|_PAGE_USER;
+ if (write)
+ result |= _PAGE_RW;
+ mask = result | _PAGE_SPECIAL;
+
+ ptep = pte_offset_kernel(&pmd, addr);
+ do {
+ pte_t pte = *ptep;
+ struct page *page;
+
+ if ((pte_val(pte) & mask) != result)
+ return 0;
+ VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
+ page = pte_page(pte);
+ if (!page_cache_get_speculative(page))
+ return 0;
+ if (unlikely(pte != *ptep)) {
+ put_page(page);
+ return 0;
+ }
+ pages[*nr] = page;
+ (*nr)++;
+
+ } while (ptep++, addr += PAGE_SIZE, addr != end);
+
+ return 1;
+}
+
+static noinline int gup_huge_pte(pte_t *ptep, struct hstate *hstate,
+ unsigned long *addr, unsigned long end,
+ int write, struct page **pages, int *nr)
+{
+ unsigned long mask;
+ unsigned long pte_end;
+ struct page *head, *page;
+ pte_t pte;
+ int refs;
+
+ pte_end = (*addr + huge_page_size(hstate)) & huge_page_mask(hstate);
+ if (pte_end < end)
+ end = pte_end;
+
+ pte = *ptep;
+ mask = _PAGE_PRESENT|_PAGE_USER;
+ if (write)
+ mask |= _PAGE_RW;
+ if ((pte_val(pte) & mask) != mask)
+ return 0;
+ /* hugepages are never "special" */
+ VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
+
+ refs = 0;
+ head = pte_page(pte);
+ page = head + ((*addr & ~huge_page_mask(hstate)) >> PAGE_SHIFT);
+ do {
+ VM_BUG_ON(compound_head(page) != head);
+ pages[*nr] = page;
+ (*nr)++;
+ page++;
+ refs++;
+ } while (*addr += PAGE_SIZE, *addr != end);
+
+ if (!page_cache_add_speculative(head, refs)) {
+ *nr -= refs;
+ return 0;
+ }
+ if (unlikely(pte != *ptep)) {
+ /* Could be optimized better */
+ while (*nr) {
+ put_page(page);
+ (*nr)--;
+ }
+ }
+
+ 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 end = start + (nr_pages << PAGE_SHIFT);
+ unsigned long addr = start;
+ unsigned long next;
+ pgd_t *pgdp;
+ int nr = 0;
+ unsigned int shift;
+
+
+ if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,
+ start, nr_pages*PAGE_SIZE)))
+ goto slow_irqon;
+
+ /* Cross a slice boundary? */
+ if (addr < SLICE_LOW_TOP) {
+ if (end > SLICE_LOW_TOP)
+ goto slow_irqon;
+
+ if (unlikely(GET_LOW_SLICE_INDEX(addr) !=
+ GET_LOW_SLICE_INDEX(end - 1)))
+ goto slow_irqon;
+ } else {
+ if (unlikely(GET_HIGH_SLICE_INDEX(addr) !=
+ GET_HIGH_SLICE_INDEX(end - 1)))
+ goto slow_irqon;
+ }
+
+ /*
+ * 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 powerpc.
+ *
+ * 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();
+
+ shift = mmu_psize_defs[get_slice_psize(mm, addr)].shift;
+
+ if (shift > PAGE_SHIFT) {
+ pte_t *ptep;
+ unsigned long a = addr;
+ unsigned long sz = ((1UL) << shift);
+ struct hstate *hstate = size_to_hstate(sz);
+
+ BUG_ON(!hstate);
+ /*
+ * XXX: could be optimized to avoid hstate
+ * lookup entirely (just use shift)
+ */
+
+ ptep = huge_pte_offset(mm, a);
+ do {
+ VM_BUG_ON(shift != mmu_psize_defs[get_slice_psize(mm, a)].shift);
+ if (!gup_huge_pte(ptep, hstate, &a, end, write, pages,
+ &nr))
+ goto slow;
+ ptep++;
+ } while (a != end);
+ } else {
+ pgdp = pgd_offset(mm, addr);
+ do {
+ pgd_t pgd = *pgdp;
+
+ VM_BUG_ON(shift != mmu_psize_defs[get_slice_psize(mm, addr)].shift);
+
+ 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();
+slow_irqon:
+ /* 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;
+ }
+}
diff -puN include/asm-powerpc/pgtable-ppc64.h~powerpc-lockless-get_user_pages include/asm-powerpc/pgtable-ppc64.h
--- a/include/asm-powerpc/pgtable-ppc64.h~powerpc-lockless-get_user_pages
+++ a/include/asm-powerpc/pgtable-ppc64.h
@@ -461,6 +461,8 @@ void pgtable_cache_init(void);
return pt;
}
+pte_t *huge_pte_offset(struct mm_struct *mm, unsigned long address);
+
#endif /* __ASSEMBLY__ */
#endif /* _ASM_POWERPC_PGTABLE_PPC64_H_ */
diff -puN include/linux/pagemap.h~powerpc-lockless-get_user_pages include/linux/pagemap.h
--- a/include/linux/pagemap.h~powerpc-lockless-get_user_pages
+++ a/include/linux/pagemap.h
@@ -143,6 +143,29 @@ static inline int page_cache_get_specula
return 1;
}
+/*
+ * Same as above, but add instead of inc (could just be merged)
+ */
+static inline int page_cache_add_speculative(struct page *page, int count)
+{
+ VM_BUG_ON(in_interrupt());
+
+#if !defined(CONFIG_SMP) && defined(CONFIG_CLASSIC_RCU)
+# ifdef CONFIG_PREEMPT
+ VM_BUG_ON(!in_atomic());
+# endif
+ VM_BUG_ON(page_count(page) == 0);
+ atomic_add(count, &page->_count);
+
+#else
+ if (unlikely(!atomic_add_unless(&page->_count, count, 0)))
+ return 0;
+#endif
+ VM_BUG_ON(PageCompound(page) && page != compound_head(page));
+
+ return 1;
+}
+
static inline int page_freeze_refs(struct page *page, int count)
{
return likely(atomic_cmpxchg(&page->_count, count, 0) == count);
_
Patches currently in -mm which might be from npiggin@xxxxxxx are
origin.patch
linux-next.patch
mspec-convert-nopfn-to-fault.patch
mspec-convert-nopfn-to-fault-fix.patch
mm-remove-nopfn.patch
mm-remove-nopfn-fix.patch
mm-remove-double-indirection-on-tlb-parameter-to-free_pgd_range-co.patch
hugetlb-guarantee-that-cow-faults-for-a-process-that-called-mmapmap_private-on-hugetlbfs-will-succeed-build-fix.patch
vma-page-offset-has-no-callees-drop-it.patch
hugetlb-factor-out-prep_new_huge_page.patch
hugetlb-modular-state-for-hugetlb-page-size.patch
hugetlb-modular-state-for-hugetlb-page-size-checkpatch-fixes.patch
hugetlb-multiple-hstates-for-multiple-page-sizes.patch
hugetlb-multiple-hstates-for-multiple-page-sizes-checkpatch-fixes.patch
hugetlbfs-per-mount-huge-page-sizes.patch
hugetlb-new-sysfs-interface.patch
hugetlb-new-sysfs-interface-fix-2.patch
hugetlb-abstract-numa-round-robin-selection.patch
mm-introduce-non-panic-alloc_bootmem.patch
mm-export-prep_compound_page-to-mm.patch
hugetlb-support-larger-than-max_order.patch
hugetlb-support-boot-allocate-different-sizes.patch
hugetlb-printk-cleanup.patch
hugetlb-introduce-pud_huge.patch
hugetlb-introduce-pud_huge-s390-fix.patch
x86-support-gb-hugepages-on-64-bit.patch
x86-add-hugepagesz-option-on-64-bit.patch
hugetlb-override-default-huge-page-size.patch
hugetlb-override-default-huge-page-size-ia64-build.patch
hugetlb-allow-arch-overried-hugepage-allocation.patch
powerpc-function-to-allocate-gigantic-hugepages.patch
powerpc-scan-device-tree-for-gigantic-pages.patch
powerpc-define-support-for-16g-hugepages.patch
fs-check-for-statfs-overflow.patch
powerpc-support-multiple-hugepage-sizes.patch
mmu-notifiers-add-list_del_init_rcu.patch
mmu-notifiers-add-mm_take_all_locks-operation.patch
mmu-notifiers-add-mm_take_all_locks-operation-checkpatch-fixes.patch
mmu-notifier-core.patch
mmu-notifier-core-fix.patch
mmu-notifier-core-fix-2.patch
x86-implement-pte_special.patch
x86-implement-pte_special-fix.patch
mm-introduce-get_user_pages_fast.patch
mm-introduce-get_user_pages_fast-fix.patch
mm-introduce-get_user_pages_fast-checkpatch-fixes.patch
x86-lockless-get_user_pages_fast.patch
x86-lockless-get_user_pages_fast-checkpatch-fixes.patch
x86-lockless-get_user_pages_fast-fix.patch
x86-lockless-get_user_pages_fast-fix-2.patch
x86-lockless-get_user_pages_fast-fix-2-fix-fix.patch
x86-lockless-get_user_pages_fast-fix-warning.patch
dio-use-get_user_pages_fast.patch
splice-use-get_user_pages_fast.patch
x86-support-1gb-hugepages-with-get_user_pages_lockless.patch
mm-readahead-scan-lockless.patch
radix-tree-add-gang_lookup_slot-gang_lookup_slot_tag.patch
mm-speculative-page-references.patch
mm-speculative-page-references-fix.patch
mm-lockless-pagecache.patch
mm-spinlock-tree_lock.patch
powerpc-implement-pte_special.patch
powerpc-implement-pte_special-update.patch
powerpc-lockless-get_user_pages.patch
vmscan-move-isolate_lru_page-to-vmscanc.patch
vmscan-move-isolate_lru_page-to-vmscanc-fix.patch
vmscan-split-lru-lists-into-anon-file-sets-splitlru-bdi_cap_swap_backed.patch
mlock-mlocked-pages-are-unevictable.patch
mlock-mlocked-pages-are-unevictable-fix.patch
mlock-mlocked-pages-are-unevictable-fix-fix.patch
mlock-mlocked-pages-are-unevictable-fix-3.patch
mlock-mlocked-pages-are-unevictable-fix-fix-munlock-page-table-walk-now-requires-mm.patch
mmap-handle-mlocked-pages-during-map-remap-unmap.patch
fix-double-unlock_page-in-2626-rc5-mm3-kernel-bug-at-mm-filemapc-575.patch
mmap-handle-mlocked-pages-during-map-remap-unmap-cleanup.patch
vmstat-mlocked-pages-statistics.patch
vmstat-mlocked-pages-statistics-fix-incorrect-mlocked-field-of-proc-meminfo.patch
reiser4.patch
likeliness-accounting-change-and-cleanup.patch
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