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GET /api/1.2/patches/2221856/?format=api
{ "id": 2221856, "url": "http://patchwork.ozlabs.org/api/1.2/patches/2221856/?format=api", "web_url": "http://patchwork.ozlabs.org/project/linux-ext4/patch/20260410120318.525653921@kernel.org/", "project": { "id": 8, "url": "http://patchwork.ozlabs.org/api/1.2/projects/8/?format=api", "name": "Linux ext4 filesystem development", "link_name": "linux-ext4", "list_id": "linux-ext4.vger.kernel.org", "list_email": "linux-ext4@vger.kernel.org", "web_url": null, "scm_url": null, "webscm_url": null, "list_archive_url": "", "list_archive_url_format": "", "commit_url_format": "" }, "msgid": "<20260410120318.525653921@kernel.org>", "list_archive_url": null, "date": "2026-04-10T12:19:37", "name": "[14/38] slub: Use prandom instead of get_cycles()", "commit_ref": null, "pull_url": null, "state": "new", "archived": false, "hash": "d76d96b82f60f87a8f31119e8bc4a0b5643c2467", "submitter": { "id": 92397, "url": "http://patchwork.ozlabs.org/api/1.2/people/92397/?format=api", "name": "Thomas Gleixner", "email": "tglx@kernel.org" }, "delegate": null, "mbox": "http://patchwork.ozlabs.org/project/linux-ext4/patch/20260410120318.525653921@kernel.org/mbox/", "series": [ { "id": 499451, "url": "http://patchwork.ozlabs.org/api/1.2/series/499451/?format=api", "web_url": "http://patchwork.ozlabs.org/project/linux-ext4/list/?series=499451", "date": "2026-04-10T12:18:27", "name": "treewide: Cleanup LATCH, CLOCK_TICK_RATE and get_cycles() [ab]use", "version": 1, "mbox": "http://patchwork.ozlabs.org/series/499451/mbox/" } ], "comments": "http://patchwork.ozlabs.org/api/patches/2221856/comments/", "check": "pending", "checks": "http://patchwork.ozlabs.org/api/patches/2221856/checks/", "tags": {}, "related": [], "headers": { "Return-Path": "\n <SRS0=guHt=CJ=vger.kernel.org=linux-ext4+bounces-15749-patchwork-incoming=ozlabs.org@ozlabs.org>", "X-Original-To": [ "incoming@patchwork.ozlabs.org", "linux-ext4@vger.kernel.org" ], "Delivered-To": [ "patchwork-incoming@legolas.ozlabs.org", "patchwork-incoming@ozlabs.org" ], "Authentication-Results": [ "legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256\n header.s=k20201202 header.b=t3jBR9hr;\n\tdkim-atps=neutral", "legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=ozlabs.org\n (client-ip=2404:9400:2221:ea00::3; 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arc=none smtp.client-ip=10.30.226.201" ], "DKIM-Signature": "v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org;\n\ts=k20201202; t=1775823580;\n\tbh=mpxbBHJF6rhzMhSEUiQvC99JYsoAEEbwdTduYzlxEPc=;\n\th=Date:From:To:Cc:Subject:References:From;\n\tb=t3jBR9hrloEPurMHDq+39Qmu/knh8sc4zRVE8/2evrp72m0jjf5ZLkiqhTfHJf3lQ\n\t UuLDw1roDamtB5PCEFrCj4Am/iqY2B6Eqxv0IhuFUbghxXFtjb45YYjGv/1iSpakD6\n\t TFwz04dexWQxc2lpHNkB6gue2paUp+SphQGzt3h2nfY78uDiPTzZOojY3e61FIsW5V\n\t nWhQqjnOO5JiF4o/mhmPEmcNABsipUeHkNa04EcUPJl0rFmYRv/1fqlaU1qeGqFkTx\n\t Wm9D7sRbThBkNSUjiYqRay+oEzZSBtooNF5Q5Yp17uiVAaos9NzjDw3gIyxmgs/heb\n\t T0VBqEkO+l/iw==", "Date": "Fri, 10 Apr 2026 14:19:37 +0200", "Message-ID": "<20260410120318.525653921@kernel.org>", "User-Agent": "quilt/0.68", "From": "Thomas Gleixner <tglx@kernel.org>", "To": "LKML <linux-kernel@vger.kernel.org>", "Cc": "Vlastimil Babka <vbabka@kernel.org>,\n linux-mm@kvack.org,\n Arnd Bergmann <arnd@arndb.de>,\n x86@kernel.org,\n Lu Baolu <baolu.lu@linux.intel.com>,\n iommu@lists.linux.dev,\n Michael Grzeschik <m.grzeschik@pengutronix.de>,\n netdev@vger.kernel.org,\n linux-wireless@vger.kernel.org,\n Herbert Xu <herbert@gondor.apana.org.au>,\n linux-crypto@vger.kernel.org,\n David Woodhouse <dwmw2@infradead.org>,\n Bernie Thompson <bernie@plugable.com>,\n linux-fbdev@vger.kernel.org,\n \"Theodore Tso\" <tytso@mit.edu>,\n linux-ext4@vger.kernel.org,\n Andrew Morton <akpm@linux-foundation.org>,\n Uladzislau Rezki <urezki@gmail.com>,\n Marco Elver <elver@google.com>,\n Dmitry Vyukov <dvyukov@google.com>,\n kasan-dev@googlegroups.com,\n Andrey Ryabinin <ryabinin.a.a@gmail.com>,\n Thomas Sailer <t.sailer@alumni.ethz.ch>,\n linux-hams@vger.kernel.org,\n \"Jason A. Donenfeld\" <Jason@zx2c4.com>,\n Richard Henderson <richard.henderson@linaro.org>,\n linux-alpha@vger.kernel.org,\n Russell King <linux@armlinux.org.uk>,\n linux-arm-kernel@lists.infradead.org,\n Catalin Marinas <catalin.marinas@arm.com>,\n Huacai Chen <chenhuacai@kernel.org>,\n loongarch@lists.linux.dev,\n Geert Uytterhoeven <geert@linux-m68k.org>,\n linux-m68k@lists.linux-m68k.org,\n Dinh Nguyen <dinguyen@kernel.org>,\n Jonas Bonn <jonas@southpole.se>,\n linux-openrisc@vger.kernel.org,\n Helge Deller <deller@gmx.de>,\n linux-parisc@vger.kernel.org,\n Michael Ellerman <mpe@ellerman.id.au>,\n linuxppc-dev@lists.ozlabs.org,\n Paul Walmsley <pjw@kernel.org>,\n linux-riscv@lists.infradead.org,\n Heiko Carstens <hca@linux.ibm.com>,\n linux-s390@vger.kernel.org,\n \"David S. Miller\" <davem@davemloft.net>,\n sparclinux@vger.kernel.org", "Subject": "[patch 14/38] slub: Use prandom instead of get_cycles()", "References": "<20260410120044.031381086@kernel.org>", "Precedence": "bulk", "X-Mailing-List": "linux-ext4@vger.kernel.org", "List-Id": "<linux-ext4.vger.kernel.org>", "List-Subscribe": "<mailto:linux-ext4+subscribe@vger.kernel.org>", "List-Unsubscribe": "<mailto:linux-ext4+unsubscribe@vger.kernel.org>", "MIME-Version": "1.0", "Content-Type": "text/plain; charset=UTF-8", "X-Spam-Status": "No, score=-1.2 required=5.0 tests=ARC_SIGNED,ARC_VALID,\n\tDKIMWL_WL_HIGH,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DMARC_PASS,\n\tMAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=disabled\n\tversion=4.0.1", "X-Spam-Checker-Version": "SpamAssassin 4.0.1 (2024-03-25) on gandalf.ozlabs.org" }, "content": "The decision whether to scan remote nodes is based on a 'random' number\nretrieved via get_cycles(). get_cycles() is about to be removed.\n\nThere is already prandom state in the code, so use that instead.\n\nSigned-off-by: Thomas Gleixner <tglx@kernel.org>\nCc: Vlastimil Babka <vbabka@kernel.org>\nCc: linux-mm@kvack.org\n---\n mm/slub.c | 37 +++++++++++++++++++++++--------------\n 1 file changed, 23 insertions(+), 14 deletions(-)", "diff": "--- a/mm/slub.c\n+++ b/mm/slub.c\n@@ -3302,6 +3302,25 @@ static inline struct slab *alloc_slab_pa\n \treturn slab;\n }\n \n+#if defined(CONFIG_SLAB_FREELIST_RANDOM) || defined(CONFIG_NUMA)\n+static DEFINE_PER_CPU(struct rnd_state, slab_rnd_state);\n+\n+static unsigned int slab_get_prandom_state(unsigned int limit)\n+{\n+\tstruct rnd_state *state;\n+\tunsigned int res;\n+\n+\t/*\n+\t * An interrupt or NMI handler might interrupt and change\n+\t * the state in the middle, but that's safe.\n+\t */\n+\tstate = &get_cpu_var(slab_rnd_state);\n+\tres = prandom_u32_state(state) % limit;\n+\tput_cpu_var(slab_rnd_state);\n+\treturn res;\n+}\n+#endif\n+\n #ifdef CONFIG_SLAB_FREELIST_RANDOM\n /* Pre-initialize the random sequence cache */\n static int init_cache_random_seq(struct kmem_cache *s)\n@@ -3365,8 +3384,6 @@ static void *next_freelist_entry(struct\n \treturn (char *)start + idx;\n }\n \n-static DEFINE_PER_CPU(struct rnd_state, slab_rnd_state);\n-\n /* Shuffle the single linked freelist based on a random pre-computed sequence */\n static bool shuffle_freelist(struct kmem_cache *s, struct slab *slab,\n \t\t\t bool allow_spin)\n@@ -3383,15 +3400,7 @@ static bool shuffle_freelist(struct kmem\n \tif (allow_spin) {\n \t\tpos = get_random_u32_below(freelist_count);\n \t} else {\n-\t\tstruct rnd_state *state;\n-\n-\t\t/*\n-\t\t * An interrupt or NMI handler might interrupt and change\n-\t\t * the state in the middle, but that's safe.\n-\t\t */\n-\t\tstate = &get_cpu_var(slab_rnd_state);\n-\t\tpos = prandom_u32_state(state) % freelist_count;\n-\t\tput_cpu_var(slab_rnd_state);\n+\t\tpos = slab_get_prandom_state(freelist_count);\n \t}\n \n \tpage_limit = slab->objects * s->size;\n@@ -3882,7 +3891,7 @@ static void *get_from_any_partial(struct\n \t * with available objects.\n \t */\n \tif (!s->remote_node_defrag_ratio ||\n-\t\t\tget_cycles() % 1024 > s->remote_node_defrag_ratio)\n+\t slab_get_prandom_state(1024) > s->remote_node_defrag_ratio)\n \t\treturn NULL;\n \n \tdo {\n@@ -7102,7 +7111,7 @@ static unsigned int\n \n \t/* see get_from_any_partial() for the defrag ratio description */\n \tif (!s->remote_node_defrag_ratio ||\n-\t\t\tget_cycles() % 1024 > s->remote_node_defrag_ratio)\n+\t slab_get_prandom_state(1024) > s->remote_node_defrag_ratio)\n \t\treturn 0;\n \n \tdo {\n@@ -8421,7 +8430,7 @@ void __init kmem_cache_init_late(void)\n \tflushwq = alloc_workqueue(\"slub_flushwq\", WQ_MEM_RECLAIM | WQ_PERCPU,\n \t\t\t\t 0);\n \tWARN_ON(!flushwq);\n-#ifdef CONFIG_SLAB_FREELIST_RANDOM\n+#if defined(CONFIG_SLAB_FREELIST_RANDOM) || defined(CONFIG_NUMA)\n \tprandom_init_once(&slab_rnd_state);\n #endif\n }\n", "prefixes": [ "14/38" ] }