linux-kernel - [RFC v2 06/34] mm, slub: unify cmpxchg_double_slab() and __cmpxchg_double

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Date:   Wed,  9 Jun 2021 13:38:35 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Christoph Lameter <cl@...ux.com>,
        David Rientjes <rientjes@...gle.com>,
        Pekka Enberg <penberg@...nel.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>
Cc:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Jann Horn <jannh@...gle.com>, Vlastimil Babka <vbabka@...e.cz>
Subject: [RFC v2 06/34] mm, slub: unify cmpxchg_double_slab() and __cmpxchg_double_slab()

These functions differ only in irq disabling in the slow path. We can create a
common function with an extra bool parameter to control the irq disabling.
As the functions are inline and the parameter compile-time constant, there
will be no runtime overhead due to this change.

Also change the DEBUG_VM based irqs disable assert to the more standard
lockdep_assert based one.

Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
---
 mm/slub.c | 62 +++++++++++++++++++++----------------------------------
 1 file changed, 24 insertions(+), 38 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index f740598696b4..76af5065baeb 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -365,13 +365,13 @@ static __always_inline void slab_unlock(struct page *page)
 	__bit_spin_unlock(PG_locked, &page->flags);
 }
 
-/* Interrupts must be disabled (for the fallback code to work right) */
-static inline bool __cmpxchg_double_slab(struct kmem_cache *s, struct page *page,
+static inline bool ___cmpxchg_double_slab(struct kmem_cache *s, struct page *page,
 		void *freelist_old, unsigned long counters_old,
 		void *freelist_new, unsigned long counters_new,
-		const char *n)
+		const char *n, bool disable_irqs)
 {
-	VM_BUG_ON(!irqs_disabled());
+	if (!disable_irqs)
+		lockdep_assert_irqs_disabled();
 #if defined(CONFIG_HAVE_CMPXCHG_DOUBLE) && \
     defined(CONFIG_HAVE_ALIGNED_STRUCT_PAGE)
 	if (s->flags & __CMPXCHG_DOUBLE) {
@@ -382,15 +382,23 @@ static inline bool __cmpxchg_double_slab(struct kmem_cache *s, struct page *page
 	} else
 #endif
 	{
+		unsigned long flags;
+
+		if (disable_irqs)
+			local_irq_save(flags);
 		slab_lock(page);
 		if (page->freelist == freelist_old &&
 					page->counters == counters_old) {
 			page->freelist = freelist_new;
 			page->counters = counters_new;
 			slab_unlock(page);
+			if (disable_irqs)
+				local_irq_restore(flags);
 			return true;
 		}
 		slab_unlock(page);
+		if (disable_irqs)
+			local_irq_restore(flags);
 	}
 
 	cpu_relax();
@@ -403,45 +411,23 @@ static inline bool __cmpxchg_double_slab(struct kmem_cache *s, struct page *page
 	return false;
 }
 
-static inline bool cmpxchg_double_slab(struct kmem_cache *s, struct page *page,
+/* Interrupts must be disabled (for the fallback code to work right) */
+static inline bool __cmpxchg_double_slab(struct kmem_cache *s, struct page *page,
 		void *freelist_old, unsigned long counters_old,
 		void *freelist_new, unsigned long counters_new,
 		const char *n)
 {
-#if defined(CONFIG_HAVE_CMPXCHG_DOUBLE) && \
-    defined(CONFIG_HAVE_ALIGNED_STRUCT_PAGE)
-	if (s->flags & __CMPXCHG_DOUBLE) {
-		if (cmpxchg_double(&page->freelist, &page->counters,
-				   freelist_old, counters_old,
-				   freelist_new, counters_new))
-			return true;
-	} else
-#endif
-	{
-		unsigned long flags;
-
-		local_irq_save(flags);
-		slab_lock(page);
-		if (page->freelist == freelist_old &&
-					page->counters == counters_old) {
-			page->freelist = freelist_new;
-			page->counters = counters_new;
-			slab_unlock(page);
-			local_irq_restore(flags);
-			return true;
-		}
-		slab_unlock(page);
-		local_irq_restore(flags);
-	}
-
-	cpu_relax();
-	stat(s, CMPXCHG_DOUBLE_FAIL);
-
-#ifdef SLUB_DEBUG_CMPXCHG
-	pr_info("%s %s: cmpxchg double redo ", n, s->name);
-#endif
+	return ___cmpxchg_double_slab(s, page, freelist_old, counters_old,
+				      freelist_new, counters_new, n, false);
+}
 
-	return false;
+static inline bool cmpxchg_double_slab(struct kmem_cache *s, struct page *page,
+		void *freelist_old, unsigned long counters_old,
+		void *freelist_new, unsigned long counters_new,
+		const char *n)
+{
+	return ___cmpxchg_double_slab(s, page, freelist_old, counters_old,
+				      freelist_new, counters_new, n, true);
 }
 
 #ifdef CONFIG_SLUB_DEBUG
-- 
2.31.1