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=-8.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, T_DKIMWL_WL_MED,USER_IN_DEF_DKIM_WL 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 951EEECDFB8 for ; Fri, 20 Jul 2018 20:02:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4115120661 for ; Fri, 20 Jul 2018 20:02:37 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="lB6bPnQQ" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4115120661 Authentication-Results: mail.kernel.org; dmarc=fail (p=reject dis=none) header.from=google.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 S1728132AbeGTUwV (ORCPT ); Fri, 20 Jul 2018 16:52:21 -0400 Received: from mail-pg1-f194.google.com ([209.85.215.194]:36571 "EHLO mail-pg1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727815AbeGTUwV (ORCPT ); Fri, 20 Jul 2018 16:52:21 -0400 Received: by mail-pg1-f194.google.com with SMTP id s7-v6so4277276pgv.3 for ; Fri, 20 Jul 2018 13:02:34 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:from:to:cc:subject:in-reply-to:message-id:references :user-agent:mime-version; bh=U95wxqtS68PgL/wEjb2QH8e7ZhgUqbKMAwpAR9PEnYo=; b=lB6bPnQQj3ZjkYGq4qveIXejJuLOa4UyQVnlyxADJc+YL4qMk/s09r5xH+OQfzcQ4v Rzdsy5j/oT/UFDCdlmtoOeBH6B1f3ySAI0EqBBCU4YjDyqEin++jQscaz99rZ2x8yYUD vqrZtt3EWceSdvR/8P8bhWUJxpTNSnkRHADmc3MSqJLzoebABZvzeeCCxqrjlm1Lg7U+ 4MaG/eBV3MQqQ4zoaAQ/fBk32lF/WToFfc1j7VzZVPOndKtcCMadwwOPd6tCF+wkLO5N nHCZO/AqLr06FUCDK5F3+x+4/K/NjERS4gUq1NrTbIKBQrvQgYmQE7cDfqgdR7a0yMCa YpOQ== 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:in-reply-to:message-id :references:user-agent:mime-version; bh=U95wxqtS68PgL/wEjb2QH8e7ZhgUqbKMAwpAR9PEnYo=; b=kP0KzWdC6fOSQIbEnIFMRnt5ml0CuA4mnBEmvOJCjheINVDb+uMz59BC5eQw+SEKPr /RXk46R/ShKXcVfWvjsaeXrLl1jaVM6F9oZLUYz0ogDUdSeweSZmsFwyInRtPHu0Qq8G s/eWNLDdQzHHq1wBTfaA/dAD1sA/jfcUnjF4lOuaFtRl40JKoEMM+8bzPWPvFXnWB1Oz 3mEdiRBqcuXAdyiM/OfDDyt49Id65j52EbkTK+vhsTSVa4vryrK7Wk4pwxix8nDIruTu nzxQsAeFW1qXTQekA++EGrZlTRqjP+kkVYZarCU+h1B84oWJDImetO0XiMXX/BbIUTQf X+Aw== X-Gm-Message-State: AOUpUlHFUkN2Twf53Kpn/zn5sdo2mZOB4i62eueo2SBO+bpBe/y2SBmJ wgLfc24VAS3o9BLiIMJstHtbvg== X-Google-Smtp-Source: AAOMgpeS8UjxyKKjGXTvN9YeSKtDMWMM6rQYvdrWMmXOImJtM3g6e3nxUVPfV/ZFNXH+rWquDUOITQ== X-Received: by 2002:a63:b349:: with SMTP id x9-v6mr3278961pgt.337.1532116954297; Fri, 20 Jul 2018 13:02:34 -0700 (PDT) Received: from [2620:15c:17:3:3a5:23a7:5e32:4598] ([2620:15c:17:3:3a5:23a7:5e32:4598]) by smtp.gmail.com with ESMTPSA id d123-v6sm3816721pfa.22.2018.07.20.13.02.33 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Fri, 20 Jul 2018 13:02:33 -0700 (PDT) Date: Fri, 20 Jul 2018 13:02:33 -0700 (PDT) From: David Rientjes X-X-Sender: rientjes@chino.kir.corp.google.com 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 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> User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: 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.