linux-kernel - [PATCH 1/4] slub: Add comments to endif pre-processor macros

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Date:   Mon, 11 Mar 2019 12:07:41 +1100
From:   "Tobin C. Harding" <tobin@...nel.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     "Tobin C. Harding" <tobin@...nel.org>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Matthew Wilcox <willy@...radead.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 1/4] slub: Add comments to endif pre-processor macros

SLUB allocator makes heavy use of ifdef/endif pre-processor macros.
The pairing of these statements is at times hard to follow e.g. if the
pair are further than a screen apart or if there are nested pairs.  We
can reduce cognitive load by adding a comment to the endif statement of
form

       #ifdef CONFIG_FOO
       ...
       #endif /* CONFIG_FOO */

Add comments to endif pre-processor macros if ifdef/endif pair is not
immediately apparent.

Signed-off-by: Tobin C. Harding <tobin@...nel.org>
---
 mm/slub.c | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index 1b08fbcb7e61..b282e22885cd 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1951,7 +1951,7 @@ static void *get_any_partial(struct kmem_cache *s, gfp_t flags,
 			}
 		}
 	} while (read_mems_allowed_retry(cpuset_mems_cookie));
-#endif
+#endif	/* CONFIG_NUMA */
 	return NULL;
 }
 
@@ -2249,7 +2249,7 @@ static void unfreeze_partials(struct kmem_cache *s,
 		discard_slab(s, page);
 		stat(s, FREE_SLAB);
 	}
-#endif
+#endif	/* CONFIG_SLUB_CPU_PARTIAL */
 }
 
 /*
@@ -2308,7 +2308,7 @@ static void put_cpu_partial(struct kmem_cache *s, struct page *page, int drain)
 		local_irq_restore(flags);
 	}
 	preempt_enable();
-#endif
+#endif	/* CONFIG_SLUB_CPU_PARTIAL */
 }
 
 static inline void flush_slab(struct kmem_cache *s, struct kmem_cache_cpu *c)
@@ -2813,7 +2813,7 @@ void *kmem_cache_alloc_node_trace(struct kmem_cache *s,
 }
 EXPORT_SYMBOL(kmem_cache_alloc_node_trace);
 #endif
-#endif
+#endif	/* CONFIG_NUMA */
 
 /*
  * Slow path handling. This may still be called frequently since objects
@@ -3845,7 +3845,7 @@ void *__kmalloc_node(size_t size, gfp_t flags, int node)
 	return ret;
 }
 EXPORT_SYMBOL(__kmalloc_node);
-#endif
+#endif	/* CONFIG_NUMA */
 
 #ifdef CONFIG_HARDENED_USERCOPY
 /*
@@ -4063,7 +4063,7 @@ void __kmemcg_cache_deactivate(struct kmem_cache *s)
 	 */
 	slab_deactivate_memcg_cache_rcu_sched(s, kmemcg_cache_deact_after_rcu);
 }
-#endif
+#endif	/* CONFIG_MEMCG */
 
 static int slab_mem_going_offline_callback(void *arg)
 {
@@ -4696,7 +4696,7 @@ static int list_locations(struct kmem_cache *s, char *buf,
 		len += sprintf(buf, "No data\n");
 	return len;
 }
-#endif
+#endif	/* CONFIG_SLUB_DEBUG */
 
 #ifdef SLUB_RESILIENCY_TEST
 static void __init resiliency_test(void)
@@ -4756,7 +4756,7 @@ static void __init resiliency_test(void)
 #ifdef CONFIG_SYSFS
 static void resiliency_test(void) {};
 #endif
-#endif
+#endif	/* SLUB_RESILIENCY_TEST */
 
 #ifdef CONFIG_SYSFS
 enum slab_stat_type {
@@ -5413,7 +5413,7 @@ STAT_ATTR(CPU_PARTIAL_ALLOC, cpu_partial_alloc);
 STAT_ATTR(CPU_PARTIAL_FREE, cpu_partial_free);
 STAT_ATTR(CPU_PARTIAL_NODE, cpu_partial_node);
 STAT_ATTR(CPU_PARTIAL_DRAIN, cpu_partial_drain);
-#endif
+#endif	/* CONFIG_SLUB_STATS */
 
 static struct attribute *slab_attrs[] = {
 	&slab_size_attr.attr,
@@ -5614,7 +5614,7 @@ static void memcg_propagate_slab_attrs(struct kmem_cache *s)
 
 	if (buffer)
 		free_page((unsigned long)buffer);
-#endif
+#endif	/* CONFIG_MEMCG */
 }
 
 static void kmem_cache_release(struct kobject *k)
-- 
2.21.0