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=-9.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT 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 19D9EC3276C for ; Thu, 2 Jan 2020 22:38:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E3C9F21835 for ; Thu, 2 Jan 2020 22:38:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1578004726; bh=GVHhkbEaOD+FtD5CQrSDcBzoKUVdkgtRPLRt16exHbk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=y9zS0L9CbdmD389Q2+XgIV4fV7OZ7TiaLiBVsCEtWghY1jU3bICXgNLeILVBFmKV6 qd05UCl50EallZKBqX49uuhIttSFNj07kDSu0L6+epzTqqLZzqhEh0jH5Dn6A9esPw GQb+Mj/2Y1LCzAX1eXEKztcpzsReiHJ7G8bpDE1w= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731346AbgABWio (ORCPT ); Thu, 2 Jan 2020 17:38:44 -0500 Received: from mail.kernel.org ([198.145.29.99]:53220 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731047AbgABWim (ORCPT ); Thu, 2 Jan 2020 17:38:42 -0500 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 6173122525; Thu, 2 Jan 2020 22:38:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1578004721; bh=GVHhkbEaOD+FtD5CQrSDcBzoKUVdkgtRPLRt16exHbk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=rrKZS2FgmRpUvKnCIINnq0Lp877llYGE7P7y6vAFXbaQU6OsOnh2Opq5JJCk1PA0O y6DQ1jgpYJP9M9cHLGeL5bF2VRDnd9+lMp/MX4+Vocv1DLVf1EuVpohAFUMu7pU6M2 wSYDTQliKApjJa+CWkD5Q7DBRFPWqQ5OKNx7oUwE= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Johannes Weiner , Chris Down , Vlastimil Babka , David Hildenbrand , Michal Hocko , Alexey Dobriyan , Andrew Morton , Linus Torvalds , Sasha Levin Subject: [PATCH 4.4 126/137] kernel: sysctl: make drop_caches write-only Date: Thu, 2 Jan 2020 23:08:19 +0100 Message-Id: <20200102220604.131048326@linuxfoundation.org> X-Mailer: git-send-email 2.24.1 In-Reply-To: <20200102220546.618583146@linuxfoundation.org> References: <20200102220546.618583146@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Johannes Weiner [ Upstream commit 204cb79ad42f015312a5bbd7012d09c93d9b46fb ] Currently, the drop_caches proc file and sysctl read back the last value written, suggesting this is somehow a stateful setting instead of a one-time command. Make it write-only, like e.g. compact_memory. While mitigating a VM problem at scale in our fleet, there was confusion about whether writing to this file will permanently switch the kernel into a non-caching mode. This influences the decision making in a tense situation, where tens of people are trying to fix tens of thousands of affected machines: Do we need a rollback strategy? What are the performance implications of operating in a non-caching state for several days? It also caused confusion when the kernel team said we may need to write the file several times to make sure it's effective ("But it already reads back 3?"). Link: http://lkml.kernel.org/r/20191031221602.9375-1-hannes@cmpxchg.org Signed-off-by: Johannes Weiner Acked-by: Chris Down Acked-by: Vlastimil Babka Acked-by: David Hildenbrand Acked-by: Michal Hocko Acked-by: Alexey Dobriyan Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Sasha Levin --- kernel/sysctl.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/sysctl.c b/kernel/sysctl.c index 24c7fe8608d0..c2dddd335d06 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -1357,7 +1357,7 @@ static struct ctl_table vm_table[] = { .procname = "drop_caches", .data = &sysctl_drop_caches, .maxlen = sizeof(int), - .mode = 0644, + .mode = 0200, .proc_handler = drop_caches_sysctl_handler, .extra1 = &one, .extra2 = &four, -- 2.20.1