[PATCHv3 20/24] mm, thp: remove compound_lock

Kirill A. Shutemov
2015-02-12T16:20:19Z

We don't need a compound lock anymore: split_huge_page() doesn't need it
anymore.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
include/linux/mm.h | 35 ------------
include/linux/page-flags.h | 12 +---
mm/debug.c | 3 -
mm/swap.c | 135 +++++++++++++++------------------------------
4 files changed, 46 insertions(+), 139 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 655d2bfabdd9..44e1d7f48158 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -398,41 +398,6 @@ static inline int is_vmalloc_or_module_addr(const void *x)

extern void kvfree(const void *addr);

-static inline void compound_lock(struct page *page)
-{
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
- VM_BUG_ON_PAGE(PageSlab(page), page);
- bit_spin_lock(PG_compound_lock, &page->flags);
-#endif
-}
-
-static inline void compound_unlock(struct page *page)
-{
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
- VM_BUG_ON_PAGE(PageSlab(page), page);
- bit_spin_unlock(PG_compound_lock, &page->flags);
-#endif
-}
-
-static inline unsigned long compound_lock_irqsave(struct page *page)
-{
- unsigned long uninitialized_var(flags);
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
- local_irq_save(flags);
- compound_lock(page);
-#endif
- return flags;
-}
-
-static inline void compound_unlock_irqrestore(struct page *page,
- unsigned long flags)
-{
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
- compound_unlock(page);
- local_irq_restore(flags);
-#endif
-}
-
static inline struct page *compound_head(struct page *page)
{
if (unlikely(PageTail(page)))
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index d471370f27e8..32e893f2fd4d 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -106,9 +106,6 @@ enum pageflags {
#ifdef CONFIG_MEMORY_FAILURE
PG_hwpoison, /* hardware poisoned page. Don't touch */
#endif
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
- PG_compound_lock,
-#endif
__NR_PAGEFLAGS,

/* Filesystems */
@@ -516,12 +513,6 @@ static inline void ClearPageSlabPfmemalloc(struct page *page)
#define __PG_MLOCKED 0
#endif

-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
-#define __PG_COMPOUND_LOCK (1 << PG_compound_lock)
-#else
-#define __PG_COMPOUND_LOCK 0
-#endif
-
/*
* Flags checked when a page is freed. Pages being freed should not have
* these flags set. It they are, there is a problem.
@@ -531,8 +522,7 @@ static inline void ClearPageSlabPfmemalloc(struct page *page)
1 << PG_private | 1 << PG_private_2 | \
1 << PG_writeback | 1 << PG_reserved | \
1 << PG_slab | 1 << PG_swapcache | 1 << PG_active | \
- 1 << PG_unevictable | __PG_MLOCKED | __PG_HWPOISON | \
- __PG_COMPOUND_LOCK)
+ 1 << PG_unevictable | __PG_MLOCKED | __PG_HWPOISON)

/*
* Flags checked when a page is prepped for return by the page allocator.
diff --git a/mm/debug.c b/mm/debug.c
index 13d2b8146ef9..4a82f639b964 100644
--- a/mm/debug.c
+++ b/mm/debug.c
@@ -45,9 +45,6 @@ static const struct trace_print_flags pageflag_names[] = {
#ifdef CONFIG_MEMORY_FAILURE
{1UL << PG_hwpoison, "hwpoison" },
#endif
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
- {1UL << PG_compound_lock, "compound_lock" },
-#endif
};

static void dump_flags(unsigned long flags,
diff --git a/mm/swap.c b/mm/swap.c
index 7b4fbb26cc2c..6c9e764f95d7 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -80,16 +80,9 @@ static void __put_compound_page(struct page *page)
(*dtor)(page);
}

-static inline bool compound_lock_needed(struct page *page)
-{
- return IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
- !PageSlab(page) && !PageHeadHuge(page);
-}
-
static void put_compound_page(struct page *page)
{
struct page *page_head;
- unsigned long flags;

if (likely(!PageTail(page))) {
if (put_page_testzero(page)) {
@@ -108,58 +101,33 @@ static void put_compound_page(struct page *page)
/* __split_huge_page_refcount can run under us */
page_head = compound_head(page);

- if (!compound_lock_needed(page_head)) {
- /*
- * If "page" is a THP tail, we must read the tail page flags
- * after the head page flags. The split_huge_page side enforces
- * write memory barriers between clearing PageTail and before
- * the head page can be freed and reallocated.
- */
- smp_rmb();
- if (likely(PageTail(page))) {
- /* __split_huge_page_refcount cannot race here. */
- VM_BUG_ON_PAGE(!PageHead(page_head), page_head);
- VM_BUG_ON_PAGE(page_mapcount(page) != 0, page);
- if (put_page_testzero(page_head)) {
- /*
- * If this is the tail of a slab compound page,
- * the tail pin must not be the last reference
- * held on the page, because the PG_slab cannot
- * be cleared before all tail pins (which skips
- * the _mapcount tail refcounting) have been
- * released. For hugetlbfs the tail pin may be
- * the last reference on the page instead,
- * because PageHeadHuge will not go away until
- * the compound page enters the buddy
- * allocator.
- */
- VM_BUG_ON_PAGE(PageSlab(page_head), page_head);
- __put_compound_page(page_head);
- }
- } else if (put_page_testzero(page))
- __put_single_page(page);
- return;
- }
-
- flags = compound_lock_irqsave(page_head);
- /* here __split_huge_page_refcount won't run anymore */
- if (likely(page != page_head && PageTail(page))) {
- bool free;
-
- free = put_page_testzero(page_head);
- compound_unlock_irqrestore(page_head, flags);
- if (free) {
- if (PageHead(page_head))
- __put_compound_page(page_head);
- else
- __put_single_page(page_head);
+ /*
+ * If "page" is a THP tail, we must read the tail page flags after the
+ * head page flags. The split_huge_page side enforces write memory
+ * barriers between clearing PageTail and before the head page can be
+ * freed and reallocated.
+ */
+ smp_rmb();
+ if (likely(PageTail(page))) {
+ /* __split_huge_page_refcount cannot race here. */
+ VM_BUG_ON_PAGE(!PageHead(page_head), page_head);
+ if (put_page_testzero(page_head)) {
+ /*
+ * If this is the tail of a slab compound page, the
+ * tail pin must not be the last reference held on the
+ * page, because the PG_slab cannot be cleared before
+ * all tail pins (which skips the _mapcount tail
+ * refcounting) have been released. For hugetlbfs the
+ * tail pin may be the last reference on the page
+ * instead, because PageHeadHuge will not go away until
+ * the compound page enters the buddy allocator.
+ */
+ VM_BUG_ON_PAGE(PageSlab(page_head), page_head);
+ __put_compound_page(page_head);
}
- } else {
- compound_unlock_irqrestore(page_head, flags);
- VM_BUG_ON_PAGE(PageTail(page), page);
- if (put_page_testzero(page))
- __put_single_page(page);
- }
+ } else if (put_page_testzero(page))
+ __put_single_page(page);
+ return;
}

void put_page(struct page *page)
@@ -178,42 +146,29 @@ EXPORT_SYMBOL(put_page);
void __get_page_tail(struct page *page)
{
struct page *page_head = compound_head(page);
- unsigned long flags;

- if (!compound_lock_needed(page_head)) {
- smp_rmb();
- if (likely(PageTail(page))) {
- /*
- * This is a hugetlbfs page or a slab page.
- * __split_huge_page_refcount cannot race here.
- */
- VM_BUG_ON_PAGE(!PageHead(page_head), page_head);
- VM_BUG_ON(page_head != page->first_page);
- VM_BUG_ON_PAGE(atomic_read(&page_head->_count) <= 0,
- page);
- atomic_inc(&page_head->_count);
- } else {
- /*
- * __split_huge_page_refcount run before us, "page" was
- * a thp tail. the split page_head has been freed and
- * reallocated as slab or hugetlbfs page of smaller
- * order (only possible if reallocated as slab on x86).
- */
- VM_BUG_ON_PAGE(atomic_read(&page->_count) <= 0, page);
- atomic_inc(&page->_count);
- }
- return;
- }
-
- flags = compound_lock_irqsave(page_head);
- /* here __split_huge_page_refcount won't run anymore */
- if (unlikely(page == page_head || !PageTail(page) ||
- !get_page_unless_zero(page_head))) {
- /* page is not part of THP page anymore */
+ smp_rmb();
+ if (likely(PageTail(page))) {
+ /*
+ * This is a hugetlbfs page or a slab page.
+ * __split_huge_page_refcount cannot race here.
+ */
+ VM_BUG_ON_PAGE(!PageHead(page_head), page_head);
+ VM_BUG_ON(page_head != page->first_page);
+ VM_BUG_ON_PAGE(atomic_read(&page_head->_count) <= 0,
+ page);
+ atomic_inc(&page_head->_count);
+ } else {
+ /*
+ * __split_huge_page_refcount run before us, "page" was
+ * a thp tail. the split page_head has been freed and
+ * reallocated as slab or hugetlbfs page of smaller
+ * order (only possible if reallocated as slab on x86).
+ */
VM_BUG_ON_PAGE(atomic_read(&page->_count) <= 0, page);
atomic_inc(&page->_count);
}
- compound_unlock_irqrestore(page_head, flags);
+ return;
}
EXPORT_SYMBOL(__get_page_tail);

--
2.1.4