From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg1-f199.google.com (mail-pg1-f199.google.com [209.85.215.199]) by kanga.kvack.org (Postfix) with ESMTP id EF6E86B0010 for ; Fri, 20 Jul 2018 16:02:35 -0400 (EDT) Received: by mail-pg1-f199.google.com with SMTP id t20-v6so6621548pgu.9 for ; Fri, 20 Jul 2018 13:02:35 -0700 (PDT) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id t69-v6sor796518pgd.355.2018.07.20.13.02.34 for (Google Transport Security); Fri, 20 Jul 2018 13:02:34 -0700 (PDT) Date: Fri, 20 Jul 2018 13:02:33 -0700 (PDT) From: David Rientjes Subject: Re: [PATCH] mm: thp: remove use_zero_page sysfs knob In-Reply-To: <20180720123243.6dfc95ba061cd06e05c0262e@linux-foundation.org> Message-ID: References: <1532110430-115278-1-git-send-email-yang.shi@linux.alibaba.com> <20180720123243.6dfc95ba061cd06e05c0262e@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Yang Shi , kirill@shutemov.name, hughd@google.com, aaron.lu@intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org 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.