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Date:   Tue, 5 Oct 2021 09:31:43 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     LKML <linux-kernel@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH] mm: don't call should_failslab() for !CONFIG_FAILSLAB

Allocations can be a very hot path, and this out-of-line function
call is noticeable.

Signed-off-by: Jens Axboe <axboe@...nel.dk>

---

diff --git a/include/linux/fault-inject.h b/include/linux/fault-inject.h
index e525f6957c49..3128d2c8b3b4 100644
--- a/include/linux/fault-inject.h
+++ b/include/linux/fault-inject.h
@@ -64,8 +64,8 @@ static inline struct dentry *fault_create_debugfs_attr(const char *name,
 
 struct kmem_cache;
 
-int should_failslab(struct kmem_cache *s, gfp_t gfpflags);
 #ifdef CONFIG_FAILSLAB
+int should_failslab(struct kmem_cache *s, gfp_t gfpflags);
 extern bool __should_failslab(struct kmem_cache *s, gfp_t gfpflags);
 #else
 static inline bool __should_failslab(struct kmem_cache *s, gfp_t gfpflags)
diff --git a/mm/slab.h b/mm/slab.h
index 58c01a34e5b8..92fd6fe01877 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -491,8 +491,10 @@ static inline struct kmem_cache *slab_pre_alloc_hook(struct kmem_cache *s,
 
 	might_alloc(flags);
 
+#ifdef CONFIG_FAILSLAB
 	if (should_failslab(s, flags))
 		return NULL;
+#endif
 
 	if (!memcg_slab_pre_alloc_hook(s, objcgp, size, flags))
 		return NULL;
diff --git a/mm/slab_common.c b/mm/slab_common.c
index ec2bb0beed75..c21bd447f237 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -1323,6 +1323,7 @@ EXPORT_TRACEPOINT_SYMBOL(kmem_cache_alloc_node);
 EXPORT_TRACEPOINT_SYMBOL(kfree);
 EXPORT_TRACEPOINT_SYMBOL(kmem_cache_free);
 
+#ifdef CONFIG_FAILSLAB
 int should_failslab(struct kmem_cache *s, gfp_t gfpflags)
 {
 	if (__should_failslab(s, gfpflags))
@@ -1330,3 +1331,4 @@ int should_failslab(struct kmem_cache *s, gfp_t gfpflags)
 	return 0;
 }
 ALLOW_ERROR_INJECTION(should_failslab, ERRNO);
+#endif

-- 
Jens Axboe

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