[rfc: cpuops adv V1 7/8] slub: Add PageSlubPartial

[Christoph Lameter]

The condition for a page being on the partial list is established by a set
of combinations of values in the page struct (inuse > 0 && freelist != NULL).

With the lockless updates that set may become temporarily incoherent.
Use an explit flag to signal that a page is on a partial list and allow
multiple adds and removes from the partial list.

Signed-off-by: Christoph Lameter <cl@xxxxxxxxx>


---
 include/linux/page-flags.h |    2 ++
 mm/slub.c                  |   25 +++++++++++++++----------
 2 files changed, 17 insertions(+), 10 deletions(-)

Index: linux-2.6/include/linux/page-flags.h
===================================================================
--- linux-2.6.orig/include/linux/page-flags.h	2010-12-02 14:53:16.000000000 -0600
+++ linux-2.6/include/linux/page-flags.h	2010-12-02 15:01:35.000000000 -0600
@@ -128,6 +128,7 @@ enum pageflags {
 
 	/* SLUB */
 	PG_slub_frozen = PG_active,
+	PG_slub_partial = PG_error,
 };
 
 #ifndef __GENERATING_BOUNDS_H
@@ -214,6 +215,7 @@ PAGEFLAG(SwapBacked, swapbacked) __CLEAR
 __PAGEFLAG(SlobFree, slob_free)
 
 __PAGEFLAG(SlubFrozen, slub_frozen)
+__PAGEFLAG(SlubPartial, slub_partial) TESTSCFLAG(SlubPartial, slub_partial)
 
 /*
  * Private page markings that may be used by the filesystem that owns the page
Index: linux-2.6/mm/slub.c
===================================================================
--- linux-2.6.orig/mm/slub.c	2010-12-02 14:58:48.000000000 -0600
+++ linux-2.6/mm/slub.c	2010-12-02 15:29:50.000000000 -0600
@@ -1308,13 +1308,15 @@ static __always_inline int slab_trylock(
 static void add_partial(struct kmem_cache_node *n,
 				struct page *page, int tail)
 {
-	spin_lock(&n->list_lock);
-	n->nr_partial++;
-	if (tail)
-		list_add_tail(&page->lru, &n->partial);
-	else
-		list_add(&page->lru, &n->partial);
-	spin_unlock(&n->list_lock);
+	if (!TestSetPageSlubPartial(page)) {
+		spin_lock(&n->list_lock);
+		n->nr_partial++;
+		if (tail)
+			list_add_tail(&page->lru, &n->partial);
+		else
+			list_add(&page->lru, &n->partial);
+		spin_unlock(&n->list_lock);
+	}
 }
 
 static inline void __remove_partial(struct kmem_cache_node *n,
@@ -1322,15 +1324,18 @@ static inline void __remove_partial(stru
 {
 	list_del(&page->lru);
 	n->nr_partial--;
+	__ClearPageSlubPartial(page);
 }
 
 static void remove_partial(struct kmem_cache *s, struct page *page)
 {
 	struct kmem_cache_node *n = get_node(s, page_to_nid(page));
 
-	spin_lock(&n->list_lock);
-	__remove_partial(n, page);
-	spin_unlock(&n->list_lock);
+	if (TestClearPageSlubPartial(page)) {
+		spin_lock(&n->list_lock);
+		__remove_partial(n, page);
+		spin_unlock(&n->list_lock);
+	}
 }
 
 /*

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