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=-2.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 8DE6CCA9ECF for ; Fri, 1 Nov 2019 11:09:06 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 4E5F0217D9 for ; Fri, 1 Nov 2019 11:09:06 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=chrisdown.name header.i=@chrisdown.name header.b="nRSM804q" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4E5F0217D9 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=chrisdown.name Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id D90F56B0005; Fri, 1 Nov 2019 07:09:05 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id D433E6B0006; Fri, 1 Nov 2019 07:09:05 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id C30136B0007; Fri, 1 Nov 2019 07:09:05 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0252.hostedemail.com [216.40.44.252]) by kanga.kvack.org (Postfix) with ESMTP id A5C856B0005 for ; Fri, 1 Nov 2019 07:09:05 -0400 (EDT) Received: from smtpin12.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with SMTP id 40A8175BC for ; Fri, 1 Nov 2019 11:09:05 +0000 (UTC) X-FDA: 76107436650.12.yard71_4f460533d2817 X-HE-Tag: yard71_4f460533d2817 X-Filterd-Recvd-Size: 3616 Received: from mail-wr1-f65.google.com (mail-wr1-f65.google.com [209.85.221.65]) by imf32.hostedemail.com (Postfix) with ESMTP for ; Fri, 1 Nov 2019 11:09:04 +0000 (UTC) Received: by mail-wr1-f65.google.com with SMTP id a11so9288634wra.6 for ; Fri, 01 Nov 2019 04:09:04 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chrisdown.name; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=PNqWAL/vcdIkzWkk07XofANRcuWQjzPIpS1/GtEbKcU=; b=nRSM804qrZvift9Sh05oWVFc4gK8vA+tN8Q5awmIhEf7D56uQzsrhVEwmH9i7r2CqC qZHIOSKKZNx2DDqZ2sLIVtBzTX34ue815t86YY1RhnRdUZShaZw722hlrxtIeFOSi+mC sepoIBwqrGvjU06MqnATXk7czNawaz2Yu2RAQ= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=PNqWAL/vcdIkzWkk07XofANRcuWQjzPIpS1/GtEbKcU=; b=sX4lQFo2I/HkkuJmW80vxS1VeHS/Yyu7tgLNQU0tmcxCkaI/HUbLTq34+AhAxHxlbv dMITLTNLgkDWBycjhXjmhFOlYFZ/MhRqFXLZGHf7JYE1RyQiWL0JfyHgABmw6K57hoBZ bH2/IdOWJGajhgOp1eoowd+VFu4D0nr47DfLJ8towxj1hj+Tso8aWft4c5GpcvMG3ZSM CExFRIWVlvhN12ARyM5ro0EDyXmu8LLwUL/T1U4E9zdgdemCXcMeL2VcYSBwUESEExQw tUXqMsY19L1NJEmB1skvO4E2QuONmXepowImP3nYaX8vudYJOCxrRmr3NkNxIq1fa92l 1Hyg== X-Gm-Message-State: APjAAAVDf35ofdmNO/m8iHHirmGeGQyqrHTsPK+oKy3pBW8XYzECfPqw j0CkuIBsIg2jdM6FbEeKf4uCjHK89Sdpyfg4 X-Google-Smtp-Source: APXvYqy2l0PDMZPx7dSHoMcIgMT8UP4V/5TqGtuFA71u3xhya0ajNZFM5P9rdj15G2bswWsroasc9Q== X-Received: by 2002:adf:c409:: with SMTP id v9mr10205437wrf.41.1572606543510; Fri, 01 Nov 2019 04:09:03 -0700 (PDT) Received: from localhost ([2620:10d:c092:180::1:f970]) by smtp.gmail.com with ESMTPSA id d4sm10304948wrc.54.2019.11.01.04.09.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 01 Nov 2019 04:09:02 -0700 (PDT) Date: Fri, 1 Nov 2019 11:09:01 +0000 From: Chris Down To: Andrew Morton Cc: Johannes Weiner , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@fb.com Subject: Re: [PATCH] kernel: sysctl: make drop_caches write-only Message-ID: <20191101110901.GB690103@chrisdown.name> References: <20191031221602.9375-1-hannes@cmpxchg.org> <20191031162825.a545a5d4d8567368501769bd@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20191031162825.a545a5d4d8567368501769bd@linux-foundation.org> User-Agent: Mutt/1.12.2 (2019-09-21) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000222, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Hm, not sure why my client didn't show this reply. Andrew Morton writes: >Risk: some (odd) userspace code will break. Fixable by manually chmodding >it back again. The only scenario I can construct in my head is that someone has built something to watch drop_caches for modification, but we already have the kmsg output for that. >Reward: very little. > >Is the reward worth the risk? There is evidence that this has already caused confusion[0] for many, judging by the number of views and votes. I think the reward is higher than stated here, since it makes the intent and lack of persistent API in the API clearer, and less likely to cause confusion in future. 0: https://unix.stackexchange.com/q/17936/10762