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 74843C00454 for ; Wed, 11 Dec 2019 15:36:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4A0D62464B for ; Wed, 11 Dec 2019 15:36:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1576078576; bh=dIfCz3Zt8PohvxBeJBhWjWv+5k+mpJwXkU+kG+LB/LA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=Xpllae6V4jVLOhJxHTyrmRdRNha/L3TCswg1KYdpl+u7NrUkr7bY8M4mU/+d1fqbo YbewEvUgiXksC9/Llp4s6/k2NRJaQCRnIaiZoG5/ycxskCYT9Dh75n2TBdh8dbYOS9 OAWvkpdRNuyPsv6e2b0qdkri4E4xzLXWiJENzKV4= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388029AbfLKPgP (ORCPT ); Wed, 11 Dec 2019 10:36:15 -0500 Received: from mail.kernel.org ([198.145.29.99]:45330 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1733101AbfLKPf4 (ORCPT ); Wed, 11 Dec 2019 10:35:56 -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 376C52464B; Wed, 11 Dec 2019 15:35:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1576078556; bh=dIfCz3Zt8PohvxBeJBhWjWv+5k+mpJwXkU+kG+LB/LA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=1e/J80Nd9RpM8lLA5qmyuZkc0N3RB/DGiQONXnef4ay88+DanFiVY7gwRdbkUOIZx NZ86XjKVAE1kWDd9ELP5SkyR4xuF7MlU2YHg0yTEEDVzYj2auTa+XvVnJJwkdA37XQ kvHs3Jqj/13345/5nrH+Lv4ysnuZWFJVTQtnILoA= 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 4.9 42/42] kernel: sysctl: make drop_caches write-only Date: Wed, 11 Dec 2019 10:35:10 -0500 Message-Id: <20191211153510.23861-42-sashal@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20191211153510.23861-1-sashal@kernel.org> References: <20191211153510.23861-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore 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 6af1ac551ea3a..34449ec0689d0 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -1398,7 +1398,7 @@ 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