From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg1-f200.google.com (mail-pg1-f200.google.com [209.85.215.200]) by kanga.kvack.org (Postfix) with ESMTP id 155A56B000A for ; Fri, 20 Jul 2018 16:38:05 -0400 (EDT) Received: by mail-pg1-f200.google.com with SMTP id u4-v6so6668847pgr.2 for ; Fri, 20 Jul 2018 13:38:05 -0700 (PDT) Received: from out30-130.freemail.mail.aliyun.com (out30-130.freemail.mail.aliyun.com. [115.124.30.130]) by mx.google.com with ESMTPS id g40-v6si2547309plb.169.2018.07.20.13.38.03 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 20 Jul 2018 13:38:03 -0700 (PDT) Subject: Re: [PATCH] mm: thp: remove use_zero_page sysfs knob 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 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: owner-linux-mm@kvack.org List-ID: 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 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?