From patchwork Sun Dec 1 01:56:08 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andrew Morton X-Patchwork-Id: 11268409 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id BEA8914B7 for ; Sun, 1 Dec 2019 01:56:12 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 8C71922B48 for ; Sun, 1 Dec 2019 01:56:12 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="OMxLvpmY" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8C71922B48 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id E0CC96B0345; Sat, 30 Nov 2019 20:56:10 -0500 (EST) Delivered-To: linux-mm-outgoing@kvack.org Received: by kanga.kvack.org (Postfix, from userid 40) id D70606B0347; Sat, 30 Nov 2019 20:56:10 -0500 (EST) X-Original-To: int-list-linux-mm@kvack.org X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id C873F6B0348; Sat, 30 Nov 2019 20:56:10 -0500 (EST) X-Original-To: linux-mm@kvack.org X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0245.hostedemail.com [216.40.44.245]) by kanga.kvack.org (Postfix) with ESMTP id A73516B0345 for ; Sat, 30 Nov 2019 20:56:10 -0500 (EST) Received: from smtpin03.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with SMTP id 5E10F180AD817 for ; Sun, 1 Dec 2019 01:56:10 +0000 (UTC) X-FDA: 76214907300.03.waste45_35dd139899d41 X-Spam-Summary: 2,0,0,1e1d4ebdb541d754,d41d8cd98f00b204,akpm@linux-foundation.org,:adobriyan@gmail.com:akpm@linux-foundation.org:chris@chrisdown.name:david@redhat.com:hannes@cmpxchg.org::mhocko@suse.com:mm-commits@vger.kernel.org:torvalds@linux-foundation.org:vbabka@suse.cz,RULES_HIT:41:355:379:800:960:967:973:988:989:1260:1263:1345:1381:1431:1437:1534:1541:1711:1730:1747:1777:1792:2198:2199:2393:2525:2553:2559:2563:2682:2685:2693:2859:2902:2933:2937:2939:2942:2945:2947:2951:2954:3022:3138:3139:3140:3141:3142:3353:3865:3866:3867:3868:3870:3871:3872:3934:3936:3938:3941:3944:3947:3950:3953:3956:3959:4250:4321:5007:6261:6653:7514:7576:8599:9025:9545:10004:10913:11026:11658:11914:12043:12048:12050:12296:12297:12438:12517:12519:12555:12679:12783:12986:13069:13311:13357:13846:14181:14384:14721:14849:21080:21451:21611:21627:21939:30045:30054:30090,0,RBL:error,CacheIP:none,Bayesian:0.5,0.5,0.5,Netcheck:none,DomainCache:0,MSF:not bulk,SPF:fp,MSBL:0,DNSBL:neutral,Custom_rules:0:0:0,LFt ime:3,LU X-HE-Tag: waste45_35dd139899d41 X-Filterd-Recvd-Size: 3104 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf36.hostedemail.com (Postfix) with ESMTP for ; Sun, 1 Dec 2019 01:56:09 +0000 (UTC) Received: from localhost.localdomain (c-73-231-172-41.hsd1.ca.comcast.net [73.231.172.41]) (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 142E2208E4; Sun, 1 Dec 2019 01:56:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1575165369; bh=InJUVethnyqo/0NLBqjrnd9yPOnRHCtiBP9Q9ZITlVI=; h=Date:From:To:Subject:From; b=OMxLvpmYWQz5KasDL0R+yHiQxdau91ibUu4WL7A6B3PeYBbX0ZDhZ6VKUw9IZSrPG E4nLr9lxc1C47ol9zMNUxaXxoALgFCESUAehDwc1BTJXQ/Xnz6U9xIN7mSGEgdCRsp 32nBAlBsszU3W3tHkSDnU8y/RERzwwH3crDLEIRA= Date: Sat, 30 Nov 2019 17:56:08 -0800 From: akpm@linux-foundation.org To: adobriyan@gmail.com, akpm@linux-foundation.org, chris@chrisdown.name, david@redhat.com, hannes@cmpxchg.org, linux-mm@kvack.org, mhocko@suse.com, mm-commits@vger.kernel.org, torvalds@linux-foundation.org, vbabka@suse.cz Subject: [patch 116/158] kernel: sysctl: make drop_caches write-only Message-ID: <20191201015608.f_Wv7r1zM%akpm@linux-foundation.org> User-Agent: s-nail v14.8.16 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: From: Johannes Weiner Subject: kernel: sysctl: make drop_caches write-only 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 --- kernel/sysctl.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/kernel/sysctl.c~kernel-sysctl-make-drop_caches-write-only +++ a/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,