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 5105EC3276D for ; Thu, 2 Jan 2020 22:50:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 248C520866 for ; Thu, 2 Jan 2020 22:50:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1578005437; bh=jBDoo+A/HTVXUC3Ugi9COLtzSfQPnNZY8ECqr33cvlY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=aq/nzutrYfzFvPZVmVIPf0Fywhq0aP31v3dJR2Ct1b7c9u9aIMxsrVeS7WyVs1o5C NcHMYrByh3vd7wsEVYzXTVCze4gpExtF3Qhj88x6Dkq+TpJa9bmZoqyo6zhjmUB6G9 6NYDlAuU7wtCj5A/wXFGt+AblVEshzh045DCLrp0= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729384AbgABWug (ORCPT ); Thu, 2 Jan 2020 17:50:36 -0500 Received: from mail.kernel.org ([198.145.29.99]:50532 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728356AbgABWZS (ORCPT ); Thu, 2 Jan 2020 17:25:18 -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 9F99721835; Thu, 2 Jan 2020 22:25:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1578003918; bh=jBDoo+A/HTVXUC3Ugi9COLtzSfQPnNZY8ECqr33cvlY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=xkZgcR5DMcbF1gjNzUZRwNA6Y7BcMp358yVL7ISDDRw6RGSH3hAm5srHtULOM75cj QhMoPF3ZAMIBqFG+mCnZCyQCzlo5a3i14If0WOtfChcuzfHTf43TSJxMI8G5Cx/2Gc AXEYi8m2fWZQgR9tiMvVkpgdJh9XQ89SGRFCpUTY= 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 4.14 53/91] kernel: sysctl: make drop_caches write-only Date: Thu, 2 Jan 2020 23:07:35 +0100 Message-Id: <20200102220437.874321828@linuxfoundation.org> X-Mailer: git-send-email 2.24.1 In-Reply-To: <20200102220356.856162165@linuxfoundation.org> References: <20200102220356.856162165@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 cfc2c0d1369a..74fc3a9d1923 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -1397,7 +1397,7 @@ 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