mm: spinlock tree_lock

mapping->tree_lock has no read lockers.  convert the lock from an rwlock
to a spinlock.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Hugh Dickins <hugh@veritas.com>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Reviewed-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>

7 files changed, 30 insertions, 31 deletions

diff --git a/mm/filemap.c b/mm/filemap.c
index feb8448..2ed8b03 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -109,7 +109,7 @@
 /*
  * Remove a page from the page cache and free it. Caller has to make
  * sure the page is locked and that nobody else uses it - or that usage
- * is safe.  The caller must hold a write_lock on the mapping's tree_lock.
+ * is safe.  The caller must hold the mapping's tree_lock.
  */
 void __remove_from_page_cache(struct page *page)
 {
@@ -141,9 +141,9 @@ void remove_from_page_cache(struct page *page)
 
 	BUG_ON(!PageLocked(page));
 
-	write_lock_irq(&mapping->tree_lock);
+	spin_lock_irq(&mapping->tree_lock);
 	__remove_from_page_cache(page);
-	write_unlock_irq(&mapping->tree_lock);
+	spin_unlock_irq(&mapping->tree_lock);
 }
 
 static int sync_page(void *word)
@@ -469,7 +469,7 @@ int add_to_page_cache_locked(struct page *page, struct address_space *mapping,
 		page->mapping = mapping;
 		page->index = offset;
 
-		write_lock_irq(&mapping->tree_lock);
+		spin_lock_irq(&mapping->tree_lock);
 		error = radix_tree_insert(&mapping->page_tree, offset, page);
 		if (likely(!error)) {
 			mapping->nrpages++;
@@ -480,7 +480,7 @@ int add_to_page_cache_locked(struct page *page, struct address_space *mapping,
 			page_cache_release(page);
 		}
 
-		write_unlock_irq(&mapping->tree_lock);
+		spin_unlock_irq(&mapping->tree_lock);
 		radix_tree_preload_end();
 	} else
 		mem_cgroup_uncharge_cache_page(page);
diff --git a/mm/migrate.c b/mm/migrate.c
index 3ca6392..153572f 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -323,7 +323,7 @@ static int migrate_page_move_mapping(struct address_space *mapping,
 		return 0;
 	}
 
-	write_lock_irq(&mapping->tree_lock);
+	spin_lock_irq(&mapping->tree_lock);
 
 	pslot = radix_tree_lookup_slot(&mapping->page_tree,
  					page_index(page));
@@ -331,12 +331,12 @@ static int migrate_page_move_mapping(struct address_space *mapping,
 	expected_count = 2 + !!PagePrivate(page);
 	if (page_count(page) != expected_count ||
 			(struct page *)radix_tree_deref_slot(pslot) != page) {
-		write_unlock_irq(&mapping->tree_lock);
+		spin_unlock_irq(&mapping->tree_lock);
 		return -EAGAIN;
 	}
 
 	if (!page_freeze_refs(page, expected_count)) {
-		write_unlock_irq(&mapping->tree_lock);
+		spin_unlock_irq(&mapping->tree_lock);
 		return -EAGAIN;
 	}
 
@@ -373,10 +373,9 @@ static int migrate_page_move_mapping(struct address_space *mapping,
 	__dec_zone_page_state(page, NR_FILE_PAGES);
 	__inc_zone_page_state(newpage, NR_FILE_PAGES);
 
-	write_unlock_irq(&mapping->tree_lock);
-	if (!PageSwapCache(newpage)) {
+	spin_unlock_irq(&mapping->tree_lock);
+	if (!PageSwapCache(newpage))
 		mem_cgroup_uncharge_cache_page(page);
-	}
 
 	return 0;
 }
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 94c6d89..24de8b6 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -1088,7 +1088,7 @@ int __set_page_dirty_nobuffers(struct page *page)
 		if (!mapping)
 			return 1;
 
-		write_lock_irq(&mapping->tree_lock);
+		spin_lock_irq(&mapping->tree_lock);
 		mapping2 = page_mapping(page);
 		if (mapping2) { /* Race with truncate? */
 			BUG_ON(mapping2 != mapping);
@@ -1102,7 +1102,7 @@ int __set_page_dirty_nobuffers(struct page *page)
 			radix_tree_tag_set(&mapping->page_tree,
 				page_index(page), PAGECACHE_TAG_DIRTY);
 		}
-		write_unlock_irq(&mapping->tree_lock);
+		spin_unlock_irq(&mapping->tree_lock);
 		if (mapping->host) {
 			/* !PageAnon && !swapper_space */
 			__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
@@ -1258,7 +1258,7 @@ int test_clear_page_writeback(struct page *page)
 		struct backing_dev_info *bdi = mapping->backing_dev_info;
 		unsigned long flags;
 
-		write_lock_irqsave(&mapping->tree_lock, flags);
+		spin_lock_irqsave(&mapping->tree_lock, flags);
 		ret = TestClearPageWriteback(page);
 		if (ret) {
 			radix_tree_tag_clear(&mapping->page_tree,
@@ -1269,7 +1269,7 @@ int test_clear_page_writeback(struct page *page)
 				__bdi_writeout_inc(bdi);
 			}
 		}
-		write_unlock_irqrestore(&mapping->tree_lock, flags);
+		spin_unlock_irqrestore(&mapping->tree_lock, flags);
 	} else {
 		ret = TestClearPageWriteback(page);
 	}
@@ -1287,7 +1287,7 @@ int test_set_page_writeback(struct page *page)
 		struct backing_dev_info *bdi = mapping->backing_dev_info;
 		unsigned long flags;
 
-		write_lock_irqsave(&mapping->tree_lock, flags);
+		spin_lock_irqsave(&mapping->tree_lock, flags);
 		ret = TestSetPageWriteback(page);
 		if (!ret) {
 			radix_tree_tag_set(&mapping->page_tree,
@@ -1300,7 +1300,7 @@ int test_set_page_writeback(struct page *page)
 			radix_tree_tag_clear(&mapping->page_tree,
 						page_index(page),
 						PAGECACHE_TAG_DIRTY);
-		write_unlock_irqrestore(&mapping->tree_lock, flags);
+		spin_unlock_irqrestore(&mapping->tree_lock, flags);
 	} else {
 		ret = TestSetPageWriteback(page);
 	}
diff --git a/mm/swap_state.c b/mm/swap_state.c
index 3e3381d..2c217e3 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -39,7 +39,7 @@ static struct backing_dev_info swap_backing_dev_info = {
 
 struct address_space swapper_space = {
 	.page_tree	= RADIX_TREE_INIT(GFP_ATOMIC|__GFP_NOWARN),
-	.tree_lock	= __RW_LOCK_UNLOCKED(swapper_space.tree_lock),
+	.tree_lock	= __SPIN_LOCK_UNLOCKED(swapper_space.tree_lock),
 	.a_ops		= &swap_aops,
 	.i_mmap_nonlinear = LIST_HEAD_INIT(swapper_space.i_mmap_nonlinear),
 	.backing_dev_info = &swap_backing_dev_info,
@@ -80,7 +80,7 @@ int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask)
 		SetPageSwapCache(page);
 		set_page_private(page, entry.val);
 
-		write_lock_irq(&swapper_space.tree_lock);
+		spin_lock_irq(&swapper_space.tree_lock);
 		error = radix_tree_insert(&swapper_space.page_tree,
 						entry.val, page);
 		if (likely(!error)) {
@@ -88,7 +88,7 @@ int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp_mask)
 			__inc_zone_page_state(page, NR_FILE_PAGES);
 			INC_CACHE_INFO(add_total);
 		}
-		write_unlock_irq(&swapper_space.tree_lock);
+		spin_unlock_irq(&swapper_space.tree_lock);
 		radix_tree_preload_end();
 
 		if (unlikely(error)) {
@@ -182,9 +182,9 @@ void delete_from_swap_cache(struct page *page)
 
 	entry.val = page_private(page);
 
-	write_lock_irq(&swapper_space.tree_lock);
+	spin_lock_irq(&swapper_space.tree_lock);
 	__delete_from_swap_cache(page);
-	write_unlock_irq(&swapper_space.tree_lock);
+	spin_unlock_irq(&swapper_space.tree_lock);
 
 	swap_free(entry);
 	page_cache_release(page);
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 2f33edb..af28393 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -369,13 +369,13 @@ int remove_exclusive_swap_page(struct page *page)
 	retval = 0;
 	if (p->swap_map[swp_offset(entry)] == 1) {
 		/* Recheck the page count with the swapcache lock held.. */
-		write_lock_irq(&swapper_space.tree_lock);
+		spin_lock_irq(&swapper_space.tree_lock);
 		if ((page_count(page) == 2) && !PageWriteback(page)) {
 			__delete_from_swap_cache(page);
 			SetPageDirty(page);
 			retval = 1;
 		}
-		write_unlock_irq(&swapper_space.tree_lock);
+		spin_unlock_irq(&swapper_space.tree_lock);
 	}
 	spin_unlock(&swap_lock);
 
diff --git a/mm/truncate.c b/mm/truncate.c
index b8961cb..e68443d 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -349,18 +349,18 @@ invalidate_complete_page2(struct address_space *mapping, struct page *page)
 	if (PagePrivate(page) && !try_to_release_page(page, GFP_KERNEL))
 		return 0;
 
-	write_lock_irq(&mapping->tree_lock);
+	spin_lock_irq(&mapping->tree_lock);
 	if (PageDirty(page))
 		goto failed;
 
 	BUG_ON(PagePrivate(page));
 	__remove_from_page_cache(page);
-	write_unlock_irq(&mapping->tree_lock);
+	spin_unlock_irq(&mapping->tree_lock);
 	ClearPageUptodate(page);
 	page_cache_release(page);	/* pagecache ref */
 	return 1;
 failed:
-	write_unlock_irq(&mapping->tree_lock);
+	spin_unlock_irq(&mapping->tree_lock);
 	return 0;
 }
 
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 0075eac..8f71761 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -399,7 +399,7 @@ static int __remove_mapping(struct address_space *mapping, struct page *page)
 	BUG_ON(!PageLocked(page));
 	BUG_ON(mapping != page_mapping(page));
 
-	write_lock_irq(&mapping->tree_lock);
+	spin_lock_irq(&mapping->tree_lock);
 	/*
 	 * The non racy check for a busy page.
 	 *
@@ -436,17 +436,17 @@ static int __remove_mapping(struct address_space *mapping, struct page *page)
 	if (PageSwapCache(page)) {
 		swp_entry_t swap = { .val = page_private(page) };
 		__delete_from_swap_cache(page);
-		write_unlock_irq(&mapping->tree_lock);
+		spin_unlock_irq(&mapping->tree_lock);
 		swap_free(swap);
 	} else {
 		__remove_from_page_cache(page);
-		write_unlock_irq(&mapping->tree_lock);
+		spin_unlock_irq(&mapping->tree_lock);
 	}
 
 	return 1;
 
 cannot_free:
-	write_unlock_irq(&mapping->tree_lock);
+	spin_unlock_irq(&mapping->tree_lock);
 	return 0;
 }