linux-kernel - [PATCH RFC 16/19] slab: remove unused PREEMPT

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Message-Id: <20251023-sheaves-for-all-v1-16-6ffa2c9941c0@suse.cz>
Date: Thu, 23 Oct 2025 15:52:38 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: Andrew Morton <akpm@...ux-foundation.org>, 
 Christoph Lameter <cl@...two.org>, David Rientjes <rientjes@...gle.com>, 
 Roman Gushchin <roman.gushchin@...ux.dev>, Harry Yoo <harry.yoo@...cle.com>
Cc: Uladzislau Rezki <urezki@...il.com>, 
 "Liam R. Howlett" <Liam.Howlett@...cle.com>, 
 Suren Baghdasaryan <surenb@...gle.com>, 
 Sebastian Andrzej Siewior <bigeasy@...utronix.de>, 
 Alexei Starovoitov <ast@...nel.org>, linux-mm@...ck.org, 
 linux-kernel@...r.kernel.org, linux-rt-devel@...ts.linux.dev, 
 bpf@...r.kernel.org, kasan-dev@...glegroups.com, 
 Vlastimil Babka <vbabka@...e.cz>
Subject: [PATCH RFC 16/19] slab: remove unused PREEMPT_RT specific macros

The macros slub_get_cpu_ptr()/slub_put_cpu_ptr() are now unused, remove
them. USE_LOCKLESS_FAST_PATH() has lost its true meaning with the code
being removed. The only remaining usage is in fact testing whether we
can assert irqs disabled, because spin_lock_irqsave() only does that on
!RT. Test for CONFIG_PREEMPT_RT instead.

Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
---
 mm/slub.c | 24 +-----------------------
 1 file changed, 1 insertion(+), 23 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index dcf28fc3a112..d55afa9b277f 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -201,28 +201,6 @@ enum slab_flags {
 	SL_pfmemalloc = PG_active,	/* Historical reasons for this bit */
 };

-/*
- * We could simply use migrate_disable()/enable() but as long as it's a
- * function call even on !PREEMPT_RT, use inline preempt_disable() there.
- */
-#ifndef CONFIG_PREEMPT_RT
-#define slub_get_cpu_ptr(var)		get_cpu_ptr(var)
-#define slub_put_cpu_ptr(var)		put_cpu_ptr(var)
-#define USE_LOCKLESS_FAST_PATH()	(true)
-#else
-#define slub_get_cpu_ptr(var)		\
-({					\
-	migrate_disable();		\
-	this_cpu_ptr(var);		\
-})
-#define slub_put_cpu_ptr(var)		\
-do {					\
-	(void)(var);			\
-	migrate_enable();		\
-} while (0)
-#define USE_LOCKLESS_FAST_PATH()	(false)
-#endif
-
 #ifndef CONFIG_SLUB_TINY
 #define __fastpath_inline __always_inline
 #else
@@ -715,7 +693,7 @@ static inline bool __slab_update_freelist(struct kmem_cache *s, struct slab *sla
 {
 	bool ret;

-	if (USE_LOCKLESS_FAST_PATH())
+	if (!IS_ENABLED(CONFIG_PREEMPT_RT))
 		lockdep_assert_irqs_disabled();

 	if (s->flags & __CMPXCHG_DOUBLE) {

-- 
2.51.1