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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 04523C433EF for ; Sun, 10 Oct 2021 08:59:25 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 336F260F4B for ; Sun, 10 Oct 2021 08:59:24 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 336F260F4B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=sina.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvack.org Received: by kanga.kvack.org (Postfix) id CAE6F6B0072; Sun, 10 Oct 2021 04:59:23 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id C5E966B0073; Sun, 10 Oct 2021 04:59:23 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id B4D5F900002; Sun, 10 Oct 2021 04:59:23 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id A64DD6B0072 for ; Sun, 10 Oct 2021 04:59:23 -0400 (EDT) Received: from smtpin16.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 5C73B31E59 for ; Sun, 10 Oct 2021 08:59:23 +0000 (UTC) X-FDA: 78679929006.16.C138B55 Received: from r3-11.sinamail.sina.com.cn (r3-11.sinamail.sina.com.cn [202.108.3.11]) by imf16.hostedemail.com (Postfix) with SMTP id 59373F002378 for ; Sun, 10 Oct 2021 08:59:20 +0000 (UTC) Received: from unknown (HELO localhost.localdomain)([123.115.166.15]) by sina.com (172.16.97.27) with ESMTP id 6162AB630002F394; Sun, 10 Oct 2021 16:59:18 +0800 (CST) X-Sender: hdanton@sina.com X-Auth-ID: hdanton@sina.com X-SMAIL-MID: 54449449283293 From: Hillf Danton To: Yu Zhao Cc: Will Deacon , Linux-MM , linux-kernel Subject: Re: [PATCH v4 01/11] mm: x86, arm64: add arch_has_hw_pte_young() Date: Sun, 10 Oct 2021 16:59:07 +0800 Message-Id: <20211010085907.1284-1-hdanton@sina.com> In-Reply-To: References: <20210818063107.2696454-1-yuzhao@google.com> <20210818063107.2696454-2-yuzhao@google.com> <20210819091923.GA15467@willie-the-truck> MIME-Version: 1.0 X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 59373F002378 X-Stat-Signature: 95pib149i6nwwr5ih85sreg38iswr78o Authentication-Results: imf16.hostedemail.com; dkim=none; dmarc=none; spf=pass (imf16.hostedemail.com: domain of hdanton@sina.com designates 202.108.3.11 as permitted sender) smtp.mailfrom=hdanton@sina.com X-HE-Tag: 1633856360-226609 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.001463, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, 19 Aug 2021 15:23:02 -0600 Yu Zhao wrote: >On Thu, Aug 19, 2021 at 3:19 AM Will Deacon wrote: >> >> How accurate does this need to be? Heterogeneous (big/little) systems = are >> very common on arm64, so the existing code enables hardware access fla= g >> unconditionally on CPUs that support it, meaning we could end up runni= ng >> on a system where some CPUs have hardware update and others do not. >> >> With your change, we only enable hardware access flag if _all_ CPUs su= pport >> it (and furthermore, we prevent late onlining of CPUs without the feat= ure >> if was detected at boot). This sacrifices a lot of flexibility, partic= ularly >> if we end up tackling CPU errata in this area in future, and it's not = clear >> that it's really required for what you're trying to do. > >It doesn't need to be accurate but then my question is how helpful it >is if it's not accurate. Alternatively to make the issue simpler, spin without arm64 included give= n that it will be revisited once MGLRU lands in the mainline tree. Hillf