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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,UNPARSEABLE_RELAY,URIBL_BLOCKED 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 0DF4EECDFB8 for ; Fri, 20 Jul 2018 20:37:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 68D7220652 for ; Fri, 20 Jul 2018 20:37:58 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 68D7220652 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728376AbeGTV1v (ORCPT ); Fri, 20 Jul 2018 17:27:51 -0400 Received: from out30-133.freemail.mail.aliyun.com ([115.124.30.133]:44611 "EHLO out30-133.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727319AbeGTV1u (ORCPT ); Fri, 20 Jul 2018 17:27:50 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R761e4;CH=green;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e07486;MF=yang.shi@linux.alibaba.com;NM=1;PH=DS;RN=7;SR=0;TI=SMTPD_---0T50UJDr_1532119068; Received: from US-143344MP.local(mailfrom:yang.shi@linux.alibaba.com fp:SMTPD_---0T50UJDr_1532119068) by smtp.aliyun-inc.com(127.0.0.1); Sat, 21 Jul 2018 04:37:50 +0800 Subject: Re: [PATCH] mm: thp: remove use_zero_page sysfs knob To: David Rientjes , Andrew Morton Cc: kirill@shutemov.name, hughd@google.com, aaron.lu@intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <1532110430-115278-1-git-send-email-yang.shi@linux.alibaba.com> <20180720123243.6dfc95ba061cd06e05c0262e@linux-foundation.org> From: Yang Shi Message-ID: <3238b5d2-fd89-a6be-0382-027a24a4d3ad@linux.alibaba.com> Date: Fri, 20 Jul 2018 13:37:47 -0700 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 7/20/18 1:02 PM, David Rientjes wrote: > On Fri, 20 Jul 2018, Andrew Morton wrote: > >>> By digging into the original review, it looks use_zero_page sysfs knob >>> was added to help ease-of-testing and give user a way to mitigate >>> refcounting overhead. >>> >>> It has been a few years since the knob was added at the first place, I >>> think we are confident that it is stable enough. And, since commit >>> 6fcb52a56ff60 ("thp: reduce usage of huge zero page's atomic counter"), >>> it looks refcounting overhead has been reduced significantly. >>> >>> Other than the above, the value of the knob is always 1 (enabled by >>> default), I'm supposed very few people turn it off by default. >>> >>> So, it sounds not worth to still keep this knob around. >> Probably OK. Might not be OK, nobody knows. >> >> It's been there for seven years so another six months won't kill us. >> How about as an intermediate step we add a printk("use_zero_page is >> scheduled for removal. Please contact linux-mm@kvack.org if you need >> it"). >> > We disable the huge zero page through this interface, there were issues > related to the huge zero page shrinker (probably best to never free a > per-node huge zero page after allocated) and CVE-2017-1000405 for huge > dirty COW. Thanks for the information. It looks the CVE has been resolved by commit a8f97366452ed491d13cf1e44241bc0b5740b1f0 ("mm, thp: Do not make page table dirty unconditionally in touch_p[mu]d()"), which is in 4.15 already. What was the shrinker related issue? I'm supposed it has been resolved, right?