[patch V2] mm/slub: Move slab initialization into irq enabled region

[Thomas Gleixner <tglx@xxxxxxxxxxxxx>]

Initializing a new slab can introduce rather large latencies because
most of the initialization runs always with interrupts disabled.

There is no point in doing so. The newly allocated slab is not visible
yet, so there is no reason to protect it against concurrent alloc/free.

Move the expensive parts of the initialization into allocate_slab(),
so for all allocations with GFP_WAIT set, interrupts are enabled.

Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Pekka Enberg <penberg@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: linux-mm@xxxxxxxxx
Cc: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
---

V2: Removed the extra NULL checks as suggested by Steven and Christoph

 mm/slub.c |   89 +++++++++++++++++++++++++++++---------------------------------
 1 file changed, 42 insertions(+), 47 deletions(-)

Index: linux/mm/slub.c
===================================================================
--- linux.orig/mm/slub.c
+++ linux/mm/slub.c
@@ -1306,6 +1306,17 @@ static inline void slab_free_hook(struct
 	kasan_slab_free(s, x);
 }
 
+static void setup_object(struct kmem_cache *s, struct page *page,
+				void *object)
+{
+	setup_object_debug(s, page, object);
+	if (unlikely(s->ctor)) {
+		kasan_unpoison_object_data(s, object);
+		s->ctor(object);
+		kasan_poison_object_data(s, object);
+	}
+}
+
 /*
  * Slab allocation and freeing
  */
@@ -1336,6 +1347,8 @@ static struct page *allocate_slab(struct
 	struct page *page;
 	struct kmem_cache_order_objects oo = s->oo;
 	gfp_t alloc_gfp;
+	void *start, *p;
+	int idx, order;
 
 	flags &= gfp_allowed_mask;
 
@@ -1359,13 +1372,13 @@ static struct page *allocate_slab(struct
 		 * Try a lower order alloc if possible
 		 */
 		page = alloc_slab_page(s, alloc_gfp, node, oo);
-
-		if (page)
-			stat(s, ORDER_FALLBACK);
+		if (unlikely(!page))
+			goto out;
+		stat(s, ORDER_FALLBACK);
 	}
 
-	if (kmemcheck_enabled && page
-		&& !(s->flags & (SLAB_NOTRACK | DEBUG_DEFAULT_FLAGS))) {
+	if (kmemcheck_enabled &&
+	    !(s->flags & (SLAB_NOTRACK | DEBUG_DEFAULT_FLAGS))) {
 		int pages = 1 << oo_order(oo);
 
 		kmemcheck_alloc_shadow(page, oo_order(oo), alloc_gfp, node);
@@ -1380,51 +1393,9 @@ static struct page *allocate_slab(struct
 			kmemcheck_mark_unallocated_pages(page, pages);
 	}
 
-	if (flags & __GFP_WAIT)
-		local_irq_disable();
-	if (!page)
-		return NULL;
-
 	page->objects = oo_objects(oo);
-	mod_zone_page_state(page_zone(page),
-		(s->flags & SLAB_RECLAIM_ACCOUNT) ?
-		NR_SLAB_RECLAIMABLE : NR_SLAB_UNRECLAIMABLE,
-		1 << oo_order(oo));
-
-	return page;
-}
-
-static void setup_object(struct kmem_cache *s, struct page *page,
-				void *object)
-{
-	setup_object_debug(s, page, object);
-	if (unlikely(s->ctor)) {
-		kasan_unpoison_object_data(s, object);
-		s->ctor(object);
-		kasan_poison_object_data(s, object);
-	}
-}
-
-static struct page *new_slab(struct kmem_cache *s, gfp_t flags, int node)
-{
-	struct page *page;
-	void *start;
-	void *p;
-	int order;
-	int idx;
-
-	if (unlikely(flags & GFP_SLAB_BUG_MASK)) {
-		pr_emerg("gfp: %u\n", flags & GFP_SLAB_BUG_MASK);
-		BUG();
-	}
-
-	page = allocate_slab(s,
-		flags & (GFP_RECLAIM_MASK | GFP_CONSTRAINT_MASK), node);
-	if (!page)
-		goto out;
 
 	order = compound_order(page);
-	inc_slabs_node(s, page_to_nid(page), page->objects);
 	page->slab_cache = s;
 	__SetPageSlab(page);
 	if (page->pfmemalloc)
@@ -1448,10 +1419,34 @@ static struct page *new_slab(struct kmem
 	page->freelist = start;
 	page->inuse = page->objects;
 	page->frozen = 1;
+
 out:
+	if (flags & __GFP_WAIT)
+		local_irq_disable();
+	if (!page)
+		return NULL;
+
+	mod_zone_page_state(page_zone(page),
+		(s->flags & SLAB_RECLAIM_ACCOUNT) ?
+		NR_SLAB_RECLAIMABLE : NR_SLAB_UNRECLAIMABLE,
+		1 << oo_order(oo));
+
+	inc_slabs_node(s, page_to_nid(page), page->objects);
+
 	return page;
 }
 
+static struct page *new_slab(struct kmem_cache *s, gfp_t flags, int node)
+{
+	if (unlikely(flags & GFP_SLAB_BUG_MASK)) {
+		pr_emerg("gfp: %u\n", flags & GFP_SLAB_BUG_MASK);
+		BUG();
+	}
+
+	return allocate_slab(s,
+		flags & (GFP_RECLAIM_MASK | GFP_CONSTRAINT_MASK), node);
+}
+
 static void __free_slab(struct kmem_cache *s, struct page *page)
 {
 	int order = compound_order(page);

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