From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f200.google.com (mail-wr0-f200.google.com [209.85.128.200]) by kanga.kvack.org (Postfix) with ESMTP id 28A3F2808A3 for ; Wed, 10 May 2017 10:57:31 -0400 (EDT) Received: by mail-wr0-f200.google.com with SMTP id g12so9738549wrg.15 for ; Wed, 10 May 2017 07:57:31 -0700 (PDT) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id z12si3734941wmh.135.2017.05.10.07.57.29 for (version=TLS1 cipher=AES128-SHA bits=128/128); Wed, 10 May 2017 07:57:30 -0700 (PDT) Date: Wed, 10 May 2017 16:57:26 +0200 From: Michal Hocko Subject: Re: [v3 0/9] parallelized "struct page" zeroing Message-ID: <20170510145726.GM31466@dhcp22.suse.cz> References: <1494003796-748672-1-git-send-email-pasha.tatashin@oracle.com> <20170509181234.GA4397@dhcp22.suse.cz> <20170510072419.GC31466@dhcp22.suse.cz> <3f5f1416-aa91-a2ff-cc89-b97fcaa3e4db@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3f5f1416-aa91-a2ff-cc89-b97fcaa3e4db@oracle.com> Sender: owner-linux-mm@kvack.org List-ID: To: Pasha Tatashin 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 On Wed 10-05-17 09:42:22, Pasha Tatashin wrote: > > > >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". Have you measured that? I do not think it would be super hard to measure. I would be quite surprised if this added much if anything at all as the whole struct page should be in the cache line already. We do set reference count and other struct members. Almost nobody should be looking at our page at this time and stealing the cache line. On the other hand a large memcpy will basically wipe everything away from the cpu cache. Or am I missing something? -- Michal Hocko SUSE Labs -- 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