From dc417c1d88306afb81cd83b974af13738b3e24c5 Mon Sep 17 00:00:00 2001
From: Ingo Molnar <>
Date: Fri, 3 Jul 2009 08:44:03 -0500
Subject: [PATCH 027/166] mm: Allow only SLUB on PREEMPT_RT

Memory allocators may disable interrupts or preemption as part of the
allocation and freeing process. For PREEMPT_RT it is important that
these sections remain deterministic and short and therefore don't depend
on the size of the memory to allocate/ free or the inner state of the

Until v3.12-RT the SLAB allocator was an option but involved several
changes to meet all the requirements. The SLUB design fits better with
PREEMPT_RT model and so the SLAB patches were dropped in the 3.12-RT
patchset. Comparing the two allocator, SLUB outperformed SLAB in both
throughput (time needed to allocate and free memory) and the maximal
latency of the system measured with cyclictest during hackbench.

SLOB was never evaluated since it was unlikely that it preforms better
than SLAB. During a quick test, the kernel crashed with SLOB enabled
during boot.

Disable SLAB and SLOB on PREEMPT_RT.

[bigeasy: commit description.]

Signed-off-by: Ingo Molnar <>
Signed-off-by: Thomas Gleixner <>
Signed-off-by: Sebastian Andrzej Siewior <>
Acked-by: Vlastimil Babka <>
 init/Kconfig |    2 ++
 1 file changed, 2 insertions(+)

Index: linux-5.15.13-rt26/init/Kconfig
@ linux-5.15.13-rt26/init/Kconfig:1904 @ choice
 config SLAB
 	bool "SLAB"
+	depends on !PREEMPT_RT
 	  The regular slab allocator that is established and known to work
@ linux-5.15.13-rt26/init/Kconfig:1925 @ config SLUB
 config SLOB
 	depends on EXPERT
 	bool "SLOB (Simple Allocator)"
+	depends on !PREEMPT_RT
 	   SLOB replaces the stock allocator with a drastically simpler
 	   allocator. SLOB is generally more space efficient but