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=-10.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable 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 848A2C2D0C6 for ; Wed, 11 Dec 2019 15:58:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5627420836 for ; Wed, 11 Dec 2019 15:58:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1576079913; bh=nqhmLgTvDrwYf+dN7astYkWp9WvFzdgSm3SH0Mprv9E=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=vT2IHC3cM5NUJsb6/VUNOX3cfXQnxoUjZ2ckRKrkzu5gDwXv/2AbZVQkbYRgwLJSx oWYuCr6v3waFaRFdG58Ut+BHbyPqgCHhoxfEi3MLw035iZ2zKiYU39mONkvrQonMom qg6yKJTPtMR+0R7Rk/2SwvZQ+/Hy44pFE/BcCPXQ= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730871AbfLKPOS (ORCPT ); Wed, 11 Dec 2019 10:14:18 -0500 Received: from mail.kernel.org ([198.145.29.99]:39462 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731121AbfLKPOS (ORCPT ); Wed, 11 Dec 2019 10:14:18 -0500 Received: from sasha-vm.mshome.net (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 884DB24658; Wed, 11 Dec 2019 15:14:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1576077257; bh=nqhmLgTvDrwYf+dN7astYkWp9WvFzdgSm3SH0Mprv9E=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=h39cdc81oeJDvV394IwbXN+Mg6GxE1mstkjtd2pU545y8U+IfgvxyUsBZBUXtTqXu pyvQhLpxCoWGoYqeQTZ1s4gpoUIrtOILBvzCv3Zli0/sSyS12+KLxobrKF2ZayD9to O92cXmdQDYhvugDZixbn4EEC8mZVNKz3PWjpoG0E= From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Johannes Weiner , Chris Down , Vlastimil Babka , David Hildenbrand , Michal Hocko , Alexey Dobriyan , Andrew Morton , Linus Torvalds , Sasha Levin Subject: [PATCH AUTOSEL 5.4 133/134] kernel: sysctl: make drop_caches write-only Date: Wed, 11 Dec 2019 10:11:49 -0500 Message-Id: <20191211151150.19073-133-sashal@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20191211151150.19073-1-sashal@kernel.org> References: <20191211151150.19073-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@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 b6f2f35d0bcf5..70665934d53e2 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -1466,7 +1466,7 @@ 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 = SYSCTL_ONE, .extra2 = &four, -- 2.20.1