linux-kernel - [PATCH] slub: Make sure cache_from

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Message-ID: <20260115130642.3419324-1-edumazet@google.com>
Date: Thu, 15 Jan 2026 13:06:42 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: Vlastimil Babka <vbabka@...e.cz>, Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-kernel <linux-kernel@...r.kernel.org>, Christoph Lameter <cl@...two.org>, 
	David Rientjes <rientjes@...gle.com>, Roman Gushchin <roman.gushchin@...ux.dev>, 
	Harry Yoo <harry.yoo@...cle.com>, Eric Dumazet <eric.dumazet@...il.com>, 
	Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH] slub: Make sure cache_from_obj() is inlined

clang ignores the inline attribute because it thinks cache_from_obj()
is too big.

Moves the slow path in a separate function (__cache_from_obj())
and use __fastpath_inline to please clang and CONFIG_SLUB_TINY configs.

This makes kmem_cache_free() and build_detached_freelist()
slightly faster.

$ size mm/slub.clang.before.o mm/slub.clang.after.o
   text	   data	    bss	    dec	    hex	filename
  77716	   7657	   4208	  89581	  15ded	mm/slub.clang.before.o
  77766	   7673	   4208	  89647	  15e2f	mm/slub.clang.after.o

$ scripts/bloat-o-meter -t mm/slub.clang.before.o mm/slub.clang.after.o
Function                                     old     new   delta
__cache_from_obj                               -     211    +211
build_detached_freelist                      542     569     +27
kmem_cache_free                              896     919     +23
cache_from_obj                               229       -    -229

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 mm/slub.c | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index 861592ac54257b9d148ff921e6d8f62aced607b3..88a842411c5c3d770ff0070b592f745832d13d1a 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -6748,15 +6748,10 @@ static inline struct kmem_cache *virt_to_cache(const void *obj)
 	return slab->slab_cache;
 }
 
-static inline struct kmem_cache *cache_from_obj(struct kmem_cache *s, void *x)
+static struct kmem_cache *__cache_from_obj(struct kmem_cache *s, void *x)
 {
-	struct kmem_cache *cachep;
+	struct kmem_cache *cachep = virt_to_cache(x);
 
-	if (!IS_ENABLED(CONFIG_SLAB_FREELIST_HARDENED) &&
-	    !kmem_cache_debug_flags(s, SLAB_CONSISTENCY_CHECKS))
-		return s;
-
-	cachep = virt_to_cache(x);
 	if (WARN(cachep && cachep != s,
 		 "%s: Wrong slab cache. %s but object is from %s\n",
 		 __func__, s->name, cachep->name))
@@ -6764,6 +6759,15 @@ static inline struct kmem_cache *cache_from_obj(struct kmem_cache *s, void *x)
 	return cachep;
 }
 
+static __fastpath_inline struct kmem_cache *cache_from_obj(struct kmem_cache *s, void *x)
+{
+	if (!IS_ENABLED(CONFIG_SLAB_FREELIST_HARDENED) &&
+	    !kmem_cache_debug_flags(s, SLAB_CONSISTENCY_CHECKS))
+		return s;
+
+	return __cache_from_obj(s, x);
+}
+
 /**
  * kmem_cache_free - Deallocate an object
  * @s: The cache the allocation was from.

base-commit: 944aacb68baf7624ab8d277d0ebf07f025ca137c
-- 
2.52.0.457.g6b5491de43-goog