From: Thomas Gleixner <tglx@kernel•org>
To: LKML <linux-kernel@vger•kernel.org>
Cc: Vlastimil Babka <vbabka@kernel•org>,
linux-mm@kvack•org, Arnd Bergmann <arnd@arndb•de>,
x86@kernel•org, Lu Baolu <baolu.lu@linux•intel.com>,
iommu@lists•linux.dev,
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Michael Ellerman <mpe@ellerman•id.au>,
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Heiko Carstens <hca@linux•ibm.com>,
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"David S. Miller" <davem@davemloft•net>,
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Subject: [patch 14/38] slub: Use prandom instead of get_cycles()
Date: Fri, 10 Apr 2026 14:19:37 +0200 [thread overview]
Message-ID: <20260410120318.525653921@kernel.org> (raw)
In-Reply-To: 20260410120044.031381086@kernel.org
The decision whether to scan remote nodes is based on a 'random' number
retrieved via get_cycles(). get_cycles() is about to be removed.
There is already prandom state in the code, so use that instead.
Signed-off-by: Thomas Gleixner <tglx@kernel•org>
Cc: Vlastimil Babka <vbabka@kernel•org>
Cc: linux-mm@kvack•org
---
mm/slub.c | 37 +++++++++++++++++++++++--------------
1 file changed, 23 insertions(+), 14 deletions(-)
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3302,6 +3302,25 @@ static inline struct slab *alloc_slab_pa
return slab;
}
+#if defined(CONFIG_SLAB_FREELIST_RANDOM) || defined(CONFIG_NUMA)
+static DEFINE_PER_CPU(struct rnd_state, slab_rnd_state);
+
+static unsigned int slab_get_prandom_state(unsigned int limit)
+{
+ struct rnd_state *state;
+ unsigned int res;
+
+ /*
+ * An interrupt or NMI handler might interrupt and change
+ * the state in the middle, but that's safe.
+ */
+ state = &get_cpu_var(slab_rnd_state);
+ res = prandom_u32_state(state) % limit;
+ put_cpu_var(slab_rnd_state);
+ return res;
+}
+#endif
+
#ifdef CONFIG_SLAB_FREELIST_RANDOM
/* Pre-initialize the random sequence cache */
static int init_cache_random_seq(struct kmem_cache *s)
@@ -3365,8 +3384,6 @@ static void *next_freelist_entry(struct
return (char *)start + idx;
}
-static DEFINE_PER_CPU(struct rnd_state, slab_rnd_state);
-
/* Shuffle the single linked freelist based on a random pre-computed sequence */
static bool shuffle_freelist(struct kmem_cache *s, struct slab *slab,
bool allow_spin)
@@ -3383,15 +3400,7 @@ static bool shuffle_freelist(struct kmem
if (allow_spin) {
pos = get_random_u32_below(freelist_count);
} else {
- struct rnd_state *state;
-
- /*
- * An interrupt or NMI handler might interrupt and change
- * the state in the middle, but that's safe.
- */
- state = &get_cpu_var(slab_rnd_state);
- pos = prandom_u32_state(state) % freelist_count;
- put_cpu_var(slab_rnd_state);
+ pos = slab_get_prandom_state(freelist_count);
}
page_limit = slab->objects * s->size;
@@ -3882,7 +3891,7 @@ static void *get_from_any_partial(struct
* with available objects.
*/
if (!s->remote_node_defrag_ratio ||
- get_cycles() % 1024 > s->remote_node_defrag_ratio)
+ slab_get_prandom_state(1024) > s->remote_node_defrag_ratio)
return NULL;
do {
@@ -7102,7 +7111,7 @@ static unsigned int
/* see get_from_any_partial() for the defrag ratio description */
if (!s->remote_node_defrag_ratio ||
- get_cycles() % 1024 > s->remote_node_defrag_ratio)
+ slab_get_prandom_state(1024) > s->remote_node_defrag_ratio)
return 0;
do {
@@ -8421,7 +8430,7 @@ void __init kmem_cache_init_late(void)
flushwq = alloc_workqueue("slub_flushwq", WQ_MEM_RECLAIM | WQ_PERCPU,
0);
WARN_ON(!flushwq);
-#ifdef CONFIG_SLAB_FREELIST_RANDOM
+#if defined(CONFIG_SLAB_FREELIST_RANDOM) || defined(CONFIG_NUMA)
prandom_init_once(&slab_rnd_state);
#endif
}
next prev parent reply other threads:[~2026-04-10 12:19 UTC|newest]
Thread overview: 69+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-10 12:18 [patch 00/38] treewide: Cleanup LATCH, CLOCK_TICK_RATE and get_cycles() [ab]use Thomas Gleixner
2026-04-10 12:18 ` [patch 01/38] percpu: Sanitize __percpu_qual include hell Thomas Gleixner
2026-04-10 12:18 ` [patch 02/38] x86: Cleanup include recursion hell Thomas Gleixner
2026-04-10 20:55 ` [patch V1.1 " Thomas Gleixner
2026-04-10 12:18 ` [patch 03/38] x86/apm: Remove last LATCH usage Thomas Gleixner
2026-04-10 12:18 ` [patch 04/38] x86: Use PIT_TICK_RATE instead of CLOCK_TICK_RATE Thomas Gleixner
2026-04-10 12:18 ` [patch 05/38] treewide: Remove CLOCK_TICK_RATE Thomas Gleixner
2026-04-15 6:40 ` Christophe Leroy (CS GROUP)
2026-04-16 11:22 ` Geert Uytterhoeven
2026-04-10 12:18 ` [patch 06/38] calibrate: Rework delay timer calibration Thomas Gleixner
2026-04-10 12:19 ` [patch 07/38] treewide: Consolidate cycles_t Thomas Gleixner
2026-04-13 9:15 ` Ojaswin Mujoo
2026-04-15 6:43 ` Christophe Leroy (CS GROUP)
2026-04-16 19:32 ` Thomas Gleixner
2026-04-16 11:22 ` Geert Uytterhoeven
2026-04-10 12:19 ` [patch 08/38] x86/tsc: Use rdtsc() instead of get_cycles() Thomas Gleixner
2026-04-10 12:19 ` [patch 09/38] iommu/vt-d: Use sched_clock() " Thomas Gleixner
2026-04-10 13:45 ` Baolu Lu
2026-04-10 15:14 ` Thomas Gleixner
2026-04-10 12:19 ` [patch 10/38] arcnet: Remove function timing code Thomas Gleixner
2026-04-13 15:29 ` David Woodhouse
2026-04-10 12:19 ` [patch 11/38] misc: sgi-gru: Remove get_cycles() [ab]use Thomas Gleixner
2026-04-10 20:56 ` [patch V1.1 " Thomas Gleixner
2026-04-10 12:19 ` [patch 12/38] wifi: wil6210: Replace get_cyles() usage Thomas Gleixner
2026-04-10 12:19 ` [patch 13/38] crypto: tcrypt: Replace get_cycles() with ktime_get() Thomas Gleixner
2026-04-10 12:19 ` Thomas Gleixner [this message]
2026-04-10 12:19 ` [patch 15/38] ptp: ptp_vmclock: Replace get_cycles() usage Thomas Gleixner
2026-04-13 15:33 ` David Woodhouse
2026-04-13 19:30 ` Arnd Bergmann
2026-04-10 12:19 ` [patch 16/38] fbdev: udlfb: Replace get_cycles() with ktime_get() Thomas Gleixner
2026-04-10 12:19 ` [patch 17/38] ext4: Replace get_cycles() usage " Thomas Gleixner
2026-04-13 14:46 ` Arnd Bergmann
2026-04-10 12:19 ` [patch 18/38] lib/tests: Replace get_cycles() " Thomas Gleixner
2026-04-16 10:24 ` Geert Uytterhoeven
2026-04-10 12:20 ` [patch 19/38] kcsan: Replace get_cycles() usage Thomas Gleixner
2026-04-10 13:39 ` Marco Elver
2026-04-10 12:20 ` [patch 20/38] kasan: sw_tags: Replace get_cycles() by random_get_entropy() Thomas Gleixner
2026-04-10 12:20 ` [patch 21/38] hamradio: baycom_epp: Remove BAYCOM_DEBUG Thomas Gleixner
2026-04-10 12:20 ` [patch 22/38] random: Provide CONFIG_ARCH_HAS_RANDOM_ENTROPY Thomas Gleixner
2026-04-10 12:20 ` [patch 23/38] alpha: Select ARCH_HAS_RANDOM_ENTROPY Thomas Gleixner
2026-04-12 13:22 ` Magnus Lindholm
2026-04-10 12:20 ` [patch 24/38] ARM: " Thomas Gleixner
2026-04-10 12:20 ` [patch 25/38] arm64: " Thomas Gleixner
2026-04-10 12:20 ` [patch 26/38] loongarch: " Thomas Gleixner
2026-04-10 12:20 ` [patch 27/38] m68k: " Thomas Gleixner
2026-04-10 15:31 ` Daniel Palmer
2026-04-16 11:22 ` Geert Uytterhoeven
2026-04-10 12:20 ` [patch 28/38] mips: " Thomas Gleixner
2026-04-13 5:47 ` Maciej W. Rozycki
2026-04-10 12:20 ` [patch 29/38] nios2: " Thomas Gleixner
2026-04-10 12:20 ` [patch 30/38] openrisc: " Thomas Gleixner
2026-04-12 8:56 ` Stafford Horne
2026-04-10 12:21 ` [patch 31/38] parisc: " Thomas Gleixner
2026-04-14 12:41 ` Helge Deller
2026-04-10 12:21 ` [patch 32/38] powerpc/spufs: Use mftb() directly Thomas Gleixner
2026-04-13 14:43 ` Arnd Bergmann
2026-04-15 6:38 ` Christophe Leroy (CS GROUP)
2026-04-21 6:48 ` Mukesh Kumar Chaurasiya
2026-04-10 12:21 ` [patch 33/38] powerpc: Select ARCH_HAS_RANDOM_ENTROPY Thomas Gleixner
2026-04-15 6:47 ` Christophe Leroy (CS GROUP)
2026-04-21 11:22 ` Mukesh Kumar Chaurasiya
2026-04-10 12:21 ` [patch 34/38] riscv: " Thomas Gleixner
2026-04-10 12:21 ` [patch 35/38] s390: " Thomas Gleixner
2026-04-16 13:42 ` Heiko Carstens
2026-04-16 19:29 ` Thomas Gleixner
2026-04-10 12:21 ` [patch 36/38] sparc: Select ARCH_HAS_RANDOM_ENTROPY for SPARC64 Thomas Gleixner
2026-04-10 12:21 ` [patch 37/38] x86: Select ARCH_HAS_RANDOM_ENTROPY Thomas Gleixner
2026-04-10 12:21 ` [patch 38/38] treewide: Remove asm/timex.h includes from generic code Thomas Gleixner
2026-04-13 14:45 ` Arnd Bergmann
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