From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-it0-f69.google.com (mail-it0-f69.google.com [209.85.214.69]) by kanga.kvack.org (Postfix) with ESMTP id 9A64C2808A3 for ; Wed, 10 May 2017 09:42:37 -0400 (EDT) Received: by mail-it0-f69.google.com with SMTP id r63so1247851itr.0 for ; Wed, 10 May 2017 06:42:37 -0700 (PDT) Received: from userp1040.oracle.com (userp1040.oracle.com. [156.151.31.81]) by mx.google.com with ESMTPS id u70si3257288itc.66.2017.05.10.06.42.36 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 10 May 2017 06:42:36 -0700 (PDT) Subject: Re: [v3 0/9] parallelized "struct page" zeroing 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 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 Sender: owner-linux-mm@kvack.org List-ID: 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 > > 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org