From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 865B0C3F2D7 for ; Tue, 3 Mar 2020 20:22:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5B26020848 for ; Tue, 3 Mar 2020 20:22:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728393AbgCCUWa convert rfc822-to-8bit (ORCPT ); Tue, 3 Mar 2020 15:22:30 -0500 Received: from Galois.linutronix.de ([193.142.43.55]:45326 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728176AbgCCUW3 (ORCPT ); Tue, 3 Mar 2020 15:22:29 -0500 Received: from bigeasy by Galois.linutronix.de with local (Exim 4.80) (envelope-from ) id 1j9E3d-0005wY-8G; Tue, 03 Mar 2020 21:22:25 +0100 Date: Tue, 3 Mar 2020 21:22:25 +0100 From: Sebastian Andrzej Siewior To: Andrew Morton Cc: Vlastimil Babka , linux-mm@kvack.org, Thomas Gleixner , Luis Chamberlain , Kees Cook , Iurii Zaikin , Mel Gorman , Linux API Subject: [PATCH 2/2 v3] mm/compaction: Disable compact_unevictable_allowed on RT Message-ID: <20200303202225.nhqc3v5gwlb7x6et@linutronix.de> References: <20200115161035.893221-1-bigeasy@linutronix.de> <4cf4507b-0632-34e6-5985-df933559af9f@suse.cz> <20200302173516.iysuejilava37psk@linutronix.de> <20200302132531.59a2c9dffe2515d78abaf909@linux-foundation.org> <20200303175910.ichnkjkgmz5y2ipb@linutronix.de> <20200303202054.gsosv7fsx2ma3cic@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8BIT In-Reply-To: <20200303202054.gsosv7fsx2ma3cic@linutronix.de> Sender: linux-api-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org Since commit 5bbe3547aa3ba ("mm: allow compaction of unevictable pages") it is allowed to examine mlocked pages and compact them by default. On -RT even minor pagefaults are problematic because it may take a few 100us to resolve them and until then the task is blocked. Make compact_unevictable_allowed = 0 default and issue a warning on RT if it is changed. Link: https://lore.kernel.org/linux-mm/20190710144138.qyn4tuttdq6h7kqx@linutronix.de/ Signed-off-by: Sebastian Andrzej Siewior --- v2…v3: - Allow to modify the value but issue a warning if it is changed. v1…v2: - Make the proc file RO instead removing it. - Mention this change in Documentation/…/vm.rst. Documentation/admin-guide/sysctl/vm.rst | 3 +++ kernel/sysctl.c | 27 ++++++++++++++++++++++++- mm/compaction.c | 4 ++++ 3 files changed, 33 insertions(+), 1 deletion(-) diff --git a/Documentation/admin-guide/sysctl/vm.rst b/Documentation/admin-guide/sysctl/vm.rst index 64aeee1009cab..0329a4d3fa9ec 100644 --- a/Documentation/admin-guide/sysctl/vm.rst +++ b/Documentation/admin-guide/sysctl/vm.rst @@ -128,6 +128,9 @@ allowed to examine the unevictable lru (mlocked pages) for pages to compact. This should be used on systems where stalls for minor page faults are an acceptable trade for large contiguous free memory. Set to 0 to prevent compaction from moving pages that are unevictable. Default value is 1. +On CONFIG_PREEMPT_RT the default value is 0 in order to avoid a page fault, due +to compaction, which would block the task from becomming active until the fault +is resolved. dirty_background_bytes diff --git a/kernel/sysctl.c b/kernel/sysctl.c index 982203101f961..3ace90b6ac57f 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -212,6 +212,11 @@ static int proc_do_cad_pid(struct ctl_table *table, int write, void __user *buffer, size_t *lenp, loff_t *ppos); static int proc_taint(struct ctl_table *table, int write, void __user *buffer, size_t *lenp, loff_t *ppos); +#ifdef CONFIG_COMPACTION +static int proc_dointvec_warn_RT_change(struct ctl_table *table, int write, + void __user *buffer, size_t *lenp, + loff_t *ppos); +#endif #endif #ifdef CONFIG_PRINTK @@ -1484,7 +1489,7 @@ static struct ctl_table vm_table[] = { .data = &sysctl_compact_unevictable_allowed, .maxlen = sizeof(int), .mode = 0644, - .proc_handler = proc_dointvec_minmax, + .proc_handler = proc_dointvec_warn_RT_change, .extra1 = SYSCTL_ZERO, .extra2 = SYSCTL_ONE, }, @@ -2572,6 +2577,26 @@ int proc_dointvec(struct ctl_table *table, int write, return do_proc_dointvec(table, write, buffer, lenp, ppos, NULL, NULL); } +#ifdef CONFIG_COMPACTION +static int proc_dointvec_warn_RT_change(struct ctl_table *table, int write, + void __user *buffer, size_t *lenp, + loff_t *ppos) +{ + int ret, old; + + if (!IS_ENABLED(CONFIG_PREEMPT_RT) || !write) + return proc_dointvec(table, write, buffer, lenp, ppos); + + old = *(int *)table->data; + ret = proc_dointvec(table, write, buffer, lenp, ppos); + if (ret) + return ret; + WARN_ONCE(old != *(int *)table->data, "sysctl attribute %s changed.", + table->procname); + return ret; +} +#endif + /** * proc_douintvec - read a vector of unsigned integers * @table: the sysctl table diff --git a/mm/compaction.c b/mm/compaction.c index 672d3c78c6abf..ba77809a1666e 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -1590,7 +1590,11 @@ typedef enum { * Allow userspace to control policy on scanning the unevictable LRU for * compactable pages. */ +#ifdef CONFIG_PREEMPT_RT +int sysctl_compact_unevictable_allowed __read_mostly = 0; +#else int sysctl_compact_unevictable_allowed __read_mostly = 1; +#endif static inline void update_fast_start_pfn(struct compact_control *cc, unsigned long pfn) -- 2.25.1