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Subject[PATCH 13/14] mm: lock_page_ref
Change the PG_nonewref operations into locking primitives and place them
so that they provide page level serialization with regard to the page_tree
operations. (basically replace the tree_lock with a per page lock).

The normal page lock has sufficiently different (and overlapping) scope and
protection rules that this second lock is needed.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
fs/buffer.c | 6 ++++--
include/linux/pagemap.h | 44 ++++++++++++++++++++++++++++++++------------
mm/filemap.c | 14 ++++++++------
mm/migrate.c | 12 ++++++------
mm/page-writeback.c | 18 ++++++++++++------
mm/swap_state.c | 14 ++++++++------
mm/swapfile.c | 6 ++++--
mm/truncate.c | 9 ++++++---
mm/vmscan.c | 14 +++++++-------
9 files changed, 87 insertions(+), 50 deletions(-)
Index: linux-2.6/include/linux/pagemap.h
===================================================================
--- linux-2.6.orig/include/linux/pagemap.h 2007-01-28 13:59:23.000000000 +0100
+++ linux-2.6/include/linux/pagemap.h 2007-01-28 14:03:21.000000000 +0100
@@ -13,6 +13,7 @@
#include <linux/gfp.h>
#include <linux/page-flags.h>
#include <linux/hardirq.h> /* for in_interrupt() */
+#include <linux/bit_spinlock.h>

/*
* Bits in mapping->flags. The lower __GFP_BITS_SHIFT bits are the page
@@ -53,28 +54,47 @@ static inline void mapping_set_gfp_mask(
#define page_cache_release(page) put_page(page)
void release_pages(struct page **pages, int nr, int cold);

-static inline void set_page_no_new_refs(struct page *page)
+static inline void lock_page_ref(struct page *page)
{
- VM_BUG_ON(PageNoNewRefs(page));
- preempt_disable();
- SetPageNoNewRefs(page);
+ bit_spin_lock(PG_nonewrefs, &page->flags);
smp_wmb();
}

-static inline void end_page_no_new_refs(struct page *page)
+static inline void unlock_page_ref(struct page *page)
{
- VM_BUG_ON(!PageNoNewRefs(page));
- smp_wmb();
- ClearPageNoNewRefs(page);
- preempt_enable();
+ bit_spin_unlock(PG_nonewrefs, &page->flags);
}

-static inline void wait_on_new_refs(struct page *page)
+static inline void wait_on_unlock_page_ref(struct page *page)
{
- while (unlikely(PageNoNewRefs(page)))
+ while (unlikely(test_bit(PG_nonewrefs, &page->flags)))
cpu_relax();
}

+#define lock_page_ref_irq(page) \
+ do { \
+ local_irq_disable(); \
+ lock_page_ref(page); \
+ } while (0)
+
+#define unlock_page_ref_irq(page) \
+ do { \
+ unlock_page_ref(page); \
+ local_irq_enable(); \
+ } while (0)
+
+#define lock_page_ref_irqsave(page, flags) \
+ do { \
+ local_irq_save(flags); \
+ lock_page_ref(page); \
+ } while (0)
+
+#define unlock_page_ref_irqrestore(page, flags) \
+ do { \
+ unlock_page_ref(page); \
+ local_irq_restore(flags); \
+ } while (0)
+
/*
* speculatively take a reference to a page.
* If the page is free (_count == 0), then _count is untouched, and 0
@@ -150,7 +170,7 @@ static inline int page_cache_get_specula
* page refcount has been raised. See below comment.
*/

- wait_on_new_refs(page);
+ wait_on_unlock_page_ref(page);

/*
* smp_rmb is to ensure the load of page->flags (for PageNoNewRefs())
Index: linux-2.6/mm/filemap.c
===================================================================
--- linux-2.6.orig/mm/filemap.c 2007-01-28 14:02:36.000000000 +0100
+++ linux-2.6/mm/filemap.c 2007-01-28 14:03:21.000000000 +0100
@@ -128,9 +128,11 @@ void remove_from_page_cache(struct page

BUG_ON(!PageLocked(page));

- spin_lock_irq(&mapping->tree_lock);
+ lock_page_ref_irq(page);
+ spin_lock(&mapping->tree_lock);
__remove_from_page_cache(page);
- spin_unlock_irq(&mapping->tree_lock);
+ spin_unlock(&mapping->tree_lock);
+ unlock_page_ref_irq(page);
}

static int sync_page(void *word)
@@ -440,8 +442,8 @@ int add_to_page_cache(struct page *page,
int error = radix_tree_preload(gfp_mask & ~__GFP_HIGHMEM);

if (error == 0) {
- set_page_no_new_refs(page);
- spin_lock_irq(&mapping->tree_lock);
+ lock_page_ref_irq(page);
+ spin_lock(&mapping->tree_lock);
error = radix_tree_insert(&mapping->page_tree, offset, page);
if (!error) {
page_cache_get(page);
@@ -451,8 +453,8 @@ int add_to_page_cache(struct page *page,
mapping_nrpages_inc(mapping);
__inc_zone_page_state(page, NR_FILE_PAGES);
}
- spin_unlock_irq(&mapping->tree_lock);
- end_page_no_new_refs(page);
+ spin_unlock(&mapping->tree_lock);
+ unlock_page_ref_irq(page);
radix_tree_preload_end();
}
return error;
Index: linux-2.6/mm/migrate.c
===================================================================
--- linux-2.6.orig/mm/migrate.c 2007-01-28 13:59:24.000000000 +0100
+++ linux-2.6/mm/migrate.c 2007-01-28 14:03:21.000000000 +0100
@@ -303,16 +303,16 @@ static int migrate_page_move_mapping(str
return 0;
}

- set_page_no_new_refs(page);
- spin_lock_irq(&mapping->tree_lock);
+ lock_page_ref_irq(page);
+ spin_lock(&mapping->tree_lock);

pslot = radix_tree_lookup_slot(&mapping->page_tree,
page_index(page));

if (page_count(page) != 2 + !!PagePrivate(page) ||
(struct page *)radix_tree_deref_slot(pslot) != page) {
- spin_unlock_irq(&mapping->tree_lock);
- end_page_no_new_refs(page);
+ spin_unlock(&mapping->tree_lock);
+ unlock_page_ref_irq(page);
return -EAGAIN;
}

@@ -329,8 +329,8 @@ static int migrate_page_move_mapping(str

radix_tree_replace_slot(pslot, newpage);
page->mapping = NULL;
- spin_unlock_irq(&mapping->tree_lock);
- end_page_no_new_refs(page);
+ spin_unlock(&mapping->tree_lock);
+ unlock_page_ref_irq(page);

/*
* Drop cache reference from old page.
Index: linux-2.6/mm/swap_state.c
===================================================================
--- linux-2.6.orig/mm/swap_state.c 2007-01-28 14:02:36.000000000 +0100
+++ linux-2.6/mm/swap_state.c 2007-01-28 14:03:21.000000000 +0100
@@ -78,8 +78,8 @@ static int __add_to_swap_cache(struct pa
BUG_ON(PagePrivate(page));
error = radix_tree_preload(gfp_mask);
if (!error) {
- set_page_no_new_refs(page);
- spin_lock_irq(&swapper_space.tree_lock);
+ lock_page_ref_irq(page);
+ spin_lock(&swapper_space.tree_lock);
error = radix_tree_insert(&swapper_space.page_tree,
entry.val, page);
if (!error) {
@@ -90,8 +90,8 @@ static int __add_to_swap_cache(struct pa
mapping_nrpages_inc(&swapper_space);
__inc_zone_page_state(page, NR_FILE_PAGES);
}
- spin_unlock_irq(&swapper_space.tree_lock);
- end_page_no_new_refs(page);
+ spin_unlock(&swapper_space.tree_lock);
+ unlock_page_ref_irq(page);
radix_tree_preload_end();
}
return error;
@@ -202,9 +202,11 @@ void delete_from_swap_cache(struct page

entry.val = page_private(page);

- spin_lock_irq(&swapper_space.tree_lock);
+ lock_page_ref_irq(page);
+ spin_lock(&swapper_space.tree_lock);
__delete_from_swap_cache(page);
- spin_unlock_irq(&swapper_space.tree_lock);
+ spin_unlock(&swapper_space.tree_lock);
+ unlock_page_ref_irq(page);

swap_free(entry);
page_cache_release(page);
Index: linux-2.6/mm/vmscan.c
===================================================================
--- linux-2.6.orig/mm/vmscan.c 2007-01-28 13:59:24.000000000 +0100
+++ linux-2.6/mm/vmscan.c 2007-01-28 14:03:21.000000000 +0100
@@ -390,8 +390,8 @@ int remove_mapping(struct address_space
BUG_ON(!PageLocked(page));
BUG_ON(mapping != page_mapping(page));

- set_page_no_new_refs(page);
- spin_lock_irq(&mapping->tree_lock);
+ lock_page_ref_irq(page);
+ spin_lock(&mapping->tree_lock);
/*
* The non racy check for a busy page.
*
@@ -426,22 +426,22 @@ int remove_mapping(struct address_space
if (PageSwapCache(page)) {
swp_entry_t swap = { .val = page_private(page) };
__delete_from_swap_cache(page);
- spin_unlock_irq(&mapping->tree_lock);
+ spin_unlock(&mapping->tree_lock);
swap_free(swap);
goto free_it;
}

__remove_from_page_cache(page);
- spin_unlock_irq(&mapping->tree_lock);
+ spin_unlock(&mapping->tree_lock);

free_it:
- end_page_no_new_refs(page);
+ unlock_page_ref_irq(page);
__put_page(page); /* The pagecache ref */
return 1;

cannot_free:
- spin_unlock_irq(&mapping->tree_lock);
- end_page_no_new_refs(page);
+ spin_unlock(&mapping->tree_lock);
+ unlock_page_ref_irq(page);
return 0;
}

Index: linux-2.6/fs/buffer.c
===================================================================
--- linux-2.6.orig/fs/buffer.c 2007-01-28 14:02:36.000000000 +0100
+++ linux-2.6/fs/buffer.c 2007-01-28 14:03:21.000000000 +0100
@@ -728,7 +728,8 @@ int __set_page_dirty_buffers(struct page
if (TestSetPageDirty(page))
return 0;

- spin_lock_irq(&mapping->tree_lock);
+ lock_page_ref_irq(page);
+ spin_lock(&mapping->tree_lock);
if (page->mapping) { /* Race with truncate? */
if (mapping_cap_account_dirty(mapping)) {
__inc_zone_page_state(page, NR_FILE_DIRTY);
@@ -737,7 +738,8 @@ int __set_page_dirty_buffers(struct page
radix_tree_tag_set(&mapping->page_tree,
page_index(page), PAGECACHE_TAG_DIRTY);
}
- spin_unlock_irq(&mapping->tree_lock);
+ spin_unlock(&mapping->tree_lock);
+ unlock_page_ref_irq(page);
__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
return 1;
}
Index: linux-2.6/mm/page-writeback.c
===================================================================
--- linux-2.6.orig/mm/page-writeback.c 2007-01-28 13:59:24.000000000 +0100
+++ linux-2.6/mm/page-writeback.c 2007-01-28 14:03:21.000000000 +0100
@@ -765,7 +765,8 @@ int __set_page_dirty_nobuffers(struct pa
if (!mapping)
return 1;

- spin_lock_irq(&mapping->tree_lock);
+ lock_page_ref_irq(page);
+ spin_lock(&mapping->tree_lock);
mapping2 = page_mapping(page);
if (mapping2) { /* Race with truncate? */
BUG_ON(mapping2 != mapping);
@@ -776,7 +777,8 @@ int __set_page_dirty_nobuffers(struct pa
radix_tree_tag_set(&mapping->page_tree,
page_index(page), PAGECACHE_TAG_DIRTY);
}
- spin_unlock_irq(&mapping->tree_lock);
+ spin_unlock(&mapping->tree_lock);
+ unlock_page_ref_irq(page);
if (mapping->host) {
/* !PageAnon && !swapper_space */
__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
@@ -913,13 +915,15 @@ int test_clear_page_writeback(struct pag
if (mapping) {
unsigned long flags;

- spin_lock_irqsave(&mapping->tree_lock, flags);
+ lock_page_ref_irqsave(page, flags);
+ spin_lock(&mapping->tree_lock);
ret = TestClearPageWriteback(page);
if (ret)
radix_tree_tag_clear(&mapping->page_tree,
page_index(page),
PAGECACHE_TAG_WRITEBACK);
- spin_unlock_irqrestore(&mapping->tree_lock, flags);
+ spin_unlock(&mapping->tree_lock);
+ unlock_page_ref_irqrestore(page, flags);
} else {
ret = TestClearPageWriteback(page);
}
@@ -934,7 +938,8 @@ int test_set_page_writeback(struct page
if (mapping) {
unsigned long flags;

- spin_lock_irqsave(&mapping->tree_lock, flags);
+ lock_page_ref_irqsave(page, flags);
+ spin_lock(&mapping->tree_lock);
ret = TestSetPageWriteback(page);
if (!ret)
radix_tree_tag_set(&mapping->page_tree,
@@ -944,7 +949,8 @@ int test_set_page_writeback(struct page
radix_tree_tag_clear(&mapping->page_tree,
page_index(page),
PAGECACHE_TAG_DIRTY);
- spin_unlock_irqrestore(&mapping->tree_lock, flags);
+ spin_unlock(&mapping->tree_lock);
+ unlock_page_ref_irqrestore(page, flags);
} else {
ret = TestSetPageWriteback(page);
}
Index: linux-2.6/mm/swapfile.c
===================================================================
--- linux-2.6.orig/mm/swapfile.c 2007-01-28 13:59:24.000000000 +0100
+++ linux-2.6/mm/swapfile.c 2007-01-28 14:03:21.000000000 +0100
@@ -367,13 +367,15 @@ int remove_exclusive_swap_page(struct pa
retval = 0;
if (p->swap_map[swp_offset(entry)] == 1) {
/* Recheck the page count with the swapcache lock held.. */
- spin_lock_irq(&swapper_space.tree_lock);
+ lock_page_ref_irq(page);
+ spin_lock(&swapper_space.tree_lock);
if ((page_count(page) == 2) && !PageWriteback(page)) {
__delete_from_swap_cache(page);
SetPageDirty(page);
retval = 1;
}
- spin_unlock_irq(&swapper_space.tree_lock);
+ spin_unlock(&swapper_space.tree_lock);
+ unlock_page_ref_irq(page);
}
spin_unlock(&swap_lock);

Index: linux-2.6/mm/truncate.c
===================================================================
--- linux-2.6.orig/mm/truncate.c 2007-01-28 14:02:36.000000000 +0100
+++ linux-2.6/mm/truncate.c 2007-01-28 14:03:21.000000000 +0100
@@ -333,18 +333,21 @@ invalidate_complete_page2(struct address
if (PagePrivate(page) && !try_to_release_page(page, GFP_KERNEL))
return 0;

- spin_lock_irq(&mapping->tree_lock);
+ lock_page_ref_irq(page);
+ spin_lock(&mapping->tree_lock);
if (PageDirty(page))
goto failed;

BUG_ON(PagePrivate(page));
__remove_from_page_cache(page);
- spin_unlock_irq(&mapping->tree_lock);
+ spin_unlock(&mapping->tree_lock);
+ unlock_page_ref_irq(page);
ClearPageUptodate(page);
page_cache_release(page); /* pagecache ref */
return 1;
failed:
- spin_unlock_irq(&mapping->tree_lock);
+ spin_unlock(&mapping->tree_lock);
+ unlock_page_ref_irq(page);
return 0;
}

--

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