linux-kernel - Re: [PATCH v5 1/2] mm: introduce helper to check slub_debug

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Date:   Mon, 5 Jul 2021 08:51:55 +0200
From:   Marco Elver <elver@...gle.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     yee.lee@...iatek.com, linux-kernel@...r.kernel.org,
        wsd_upstream@...iatek.com, nicholas.Tang@...iatek.com,
        Kuan-Ying.lee@...iatek.com, chinwen.chang@...iatek.com,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Matthias Brugger <matthias.bgg@...il.com>,
        "open list:SLAB ALLOCATOR" <linux-mm@...ck.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>
Subject: Re: [PATCH v5 1/2] mm: introduce helper to check slub_debug_enabled

On Mon, Jul 05, 2021 at 04:20AM +0100, Matthew Wilcox wrote:
> On Mon, Jul 05, 2021 at 10:40:57AM +0800, yee.lee@...iatek.com wrote:
> > From: Marco Elver <elver@...gle.com>
> > 
> > Introduce a helper to check slub_debug_enabled, so that we can confine
> > the use of #ifdef to the definition of the slub_debug_enabled_unlikely()
> > helper.
> 
> We don't usually embed '_unlikely' in function names; we
> just do:
> 
> static inline bool slub_debug_enabled(void)
> {
> 	return static_branch_unlikely(&slub_debug_enabled);
> }

The names are identical, this obviously won't work:

In file included from mm/slub.c:21:
mm/slab.h:219:20: error: ‘slub_debug_enabled’ redeclared as different kind of symbol
  219 | static inline bool slub_debug_enabled(void)

But it seems that someone had the same idea, and this merge window got a
__slub_debug_enabled() with 792702911f58.

Yee, can you replace this patch with the below:

From: Marco Elver <elver@...gle.com>
Date: Wed, 30 Jun 2021 20:56:57 +0200
Subject: [PATCH] mm: move helper to check slub_debug_enabled

Move the helper to check slub_debug_enabled, so that we can confine
the use of #ifdef outside slub.c as well.

Signed-off-by: Marco Elver <elver@...gle.com>
---
v6:
* Move helper instead of introducing a new one.
---
 mm/slab.h | 15 +++++++++++----
 mm/slub.c | 14 --------------
 2 files changed, 11 insertions(+), 18 deletions(-)

diff --git a/mm/slab.h b/mm/slab.h
index 67e06637ff2e..f997fd5e42c8 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -216,10 +216,18 @@ DECLARE_STATIC_KEY_FALSE(slub_debug_enabled);
 #endif
 extern void print_tracking(struct kmem_cache *s, void *object);
 long validate_slab_cache(struct kmem_cache *s);
+static inline bool __slub_debug_enabled(void)
+{
+	return static_branch_unlikely(&slub_debug_enabled);
+}
 #else
 static inline void print_tracking(struct kmem_cache *s, void *object)
 {
 }
+static inline bool __slub_debug_enabled(void)
+{
+	return false;
+}
 #endif
 
 /*
@@ -229,11 +237,10 @@ static inline void print_tracking(struct kmem_cache *s, void *object)
  */
 static inline bool kmem_cache_debug_flags(struct kmem_cache *s, slab_flags_t flags)
 {
-#ifdef CONFIG_SLUB_DEBUG
-	VM_WARN_ON_ONCE(!(flags & SLAB_DEBUG_FLAGS));
-	if (static_branch_unlikely(&slub_debug_enabled))
+	if (IS_ENABLED(CONFIG_SLUB_DEBUG))
+		VM_WARN_ON_ONCE(!(flags & SLAB_DEBUG_FLAGS));
+	if (__slub_debug_enabled())
 		return s->flags & flags;
-#endif
 	return false;
 }
 
diff --git a/mm/slub.c b/mm/slub.c
index 2ee43ff667a5..090fa14628f9 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -119,25 +119,11 @@
  */
 
 #ifdef CONFIG_SLUB_DEBUG
-
 #ifdef CONFIG_SLUB_DEBUG_ON
 DEFINE_STATIC_KEY_TRUE(slub_debug_enabled);
 #else
 DEFINE_STATIC_KEY_FALSE(slub_debug_enabled);
 #endif
-
-static inline bool __slub_debug_enabled(void)
-{
-	return static_branch_unlikely(&slub_debug_enabled);
-}
-
-#else		/* CONFIG_SLUB_DEBUG */
-
-static inline bool __slub_debug_enabled(void)
-{
-	return false;
-}
-
 #endif		/* CONFIG_SLUB_DEBUG */
 
 static inline bool kmem_cache_debug(struct kmem_cache *s)
-- 
2.32.0.93.g670b81a890-goog