From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753286AbdEJNmn (ORCPT ); Wed, 10 May 2017 09:42:43 -0400 Received: from userp1040.oracle.com ([156.151.31.81]:27195 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751419AbdEJNml (ORCPT ); Wed, 10 May 2017 09:42:41 -0400 Subject: Re: [v3 0/9] parallelized "struct page" zeroing To: Michal Hocko Cc: linux-kernel@vger.kernel.org, sparclinux@vger.kernel.org, linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, borntraeger@de.ibm.com, heiko.carstens@de.ibm.com, davem@davemloft.net References: <1494003796-748672-1-git-send-email-pasha.tatashin@oracle.com> <20170509181234.GA4397@dhcp22.suse.cz> <20170510072419.GC31466@dhcp22.suse.cz> From: Pasha Tatashin Message-ID: <3f5f1416-aa91-a2ff-cc89-b97fcaa3e4db@oracle.com> Date: Wed, 10 May 2017 09:42:22 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.1.0 MIME-Version: 1.0 In-Reply-To: <20170510072419.GC31466@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Source-IP: userv0021.oracle.com [156.151.31.71] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > > Well, I didn't object to this particular part. I was mostly concerned > about > http://lkml.kernel.org/r/1494003796-748672-4-git-send-email-pasha.tatashin@oracle.com > and the "zero" argument for other functions. I guess we can do without > that. I _think_ that we should simply _always_ initialize the page at the > __init_single_page time rather than during the allocation. That would > require dropping __GFP_ZERO for non-memblock allocations. Or do you > think we could regress for single threaded initialization? > Hi Michal, Thats exactly right, I am worried that we will regress when there is no parallelized initialization of "struct pages" if we force unconditionally do memset() in __init_single_page(). The overhead of calling memset() on a smaller chunks (64-bytes) may cause the regression, this is why I opted only for parallelized case to zero this metadata. This way, we are guaranteed to see great improvements from this change without having regressions on platforms and builds that do not support parallelized initialization of "struct pages". However, on some chips such as latest SPARCs it is beneficial to have memset() right inside __init_single_page() even for single threaded case, because it can act as a prefetch on chips with optimized block initialized store instructions. Pasha