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=-0.6 required=3.0 tests=DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,T_DKIM_INVALID 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 93900ECE561 for ; Wed, 19 Sep 2018 01:18:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1A805214DD for ; Wed, 19 Sep 2018 01:18:30 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="key not found in DNS" (0-bit key) header.d=codeaurora.org header.i=@codeaurora.org header.b="opm6Meyv"; dkim=fail reason="key not found in DNS" (0-bit key) header.d=codeaurora.org header.i=@codeaurora.org header.b="cauwfVMm" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1A805214DD Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=codeaurora.org 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 S1730688AbeISGxo (ORCPT ); Wed, 19 Sep 2018 02:53:44 -0400 Received: from smtp.codeaurora.org ([198.145.29.96]:44220 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728226AbeISGxo (ORCPT ); Wed, 19 Sep 2018 02:53:44 -0400 Received: by smtp.codeaurora.org (Postfix, from userid 1000) id F0011607F4; Wed, 19 Sep 2018 01:18:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=codeaurora.org; s=default; t=1537319906; bh=pryowjq4fwdgXB4+CQaOYijb3cewvvkFgSoSbm4jCjU=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=opm6Meyv4npa/G/2JH+2YaqUjt3ZPiGhDcaYW8HJiAv6Mmq+6JPjJfprKFAQbhE3c D2klrBoTE08N0FDrjqPdX8YdYl9aQiNO0dL3CEefvCnzoj4h/iPmTkbONyKDAGfGHl Ma5Q5yejORH98XRBjDhEEj/ifamdFV4itJcl6GQs= Received: from mail.codeaurora.org (localhost.localdomain [127.0.0.1]) by smtp.codeaurora.org (Postfix) with ESMTP id C4E5E607F4; Wed, 19 Sep 2018 01:18:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=codeaurora.org; s=default; t=1537319905; bh=pryowjq4fwdgXB4+CQaOYijb3cewvvkFgSoSbm4jCjU=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=cauwfVMmwtLWyfLi8nB/JuUrcDrGaJSGyPDRruLEnEwujjw/26yzxmb+k/NxYn/Zr frFUz8F55Be2nTspW6dbQSljlVUs6YXzi8sojdiVU9oziRBPxF3Nonpxkn12V1YhEk MSOCEHKHK4DWiBoTBfB/FOECpvjd3xxM7fXtnWc4= MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Wed, 19 Sep 2018 06:48:25 +0530 From: Arun KS To: Michal Hocko Cc: Balbir Singh , akpm@linux-foundation.org, dan.j.williams@intel.com, vbabka@suse.cz, pasha.tatashin@oracle.com, iamjoonsoo.kim@lge.com, osalvador@suse.de, malat@debian.org, gregkh@linuxfoundation.org, yasu.isimatu@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, arunks.linux@gmail.com, vinmenon@codeaurora.org Subject: Re: [RFC] memory_hotplug: Free pages as pageblock_order In-Reply-To: <20180914091053.GJ20287@dhcp22.suse.cz> References: <1536744405-16752-1-git-send-email-arunks@codeaurora.org> <20180912103853.GC10951@dhcp22.suse.cz> <20180912125743.GB8537@350D> <20180912131724.GH10951@dhcp22.suse.cz> <9d8dfd50046036a7b4e730738940014d@codeaurora.org> <20180914091053.GJ20287@dhcp22.suse.cz> Message-ID: <28e613e9a092a434cfa9b38f7b0f8eea@codeaurora.org> X-Sender: arunks@codeaurora.org User-Agent: Roundcube Webmail/1.2.5 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2018-09-14 14:40, Michal Hocko wrote: > On Wed 12-09-18 20:12:30, Arun KS wrote: >> On 2018-09-12 18:47, Michal Hocko wrote: >> > On Wed 12-09-18 22:57:43, Balbir Singh wrote: >> > > On Wed, Sep 12, 2018 at 12:38:53PM +0200, Michal Hocko wrote: >> > > > On Wed 12-09-18 14:56:45, Arun KS wrote: >> > > > > When free pages are done with pageblock_order, time spend on >> > > > > coalescing pages by buddy allocator can be reduced. With >> > > > > section size of 256MB, hot add latency of a single section >> > > > > shows improvement from 50-60 ms to less than 1 ms, hence >> > > > > improving the hot add latency by 60%. >> > > > >> > > > Where does the improvement come from? You are still doing the same >> > > > amount of work except that the number of callbacks is lower. Is this the >> > > > real source of 60% improvement? >> > > > >> > > >> > > It looks like only the first page of the pageblock is initialized, is >> > > some of the cost amortized in terms of doing one initialization for >> > > the page with order (order) and then relying on split_page and helpers >> > > to do the rest? Of course the number of callbacks reduce by a >> > > significant >> > > number as well. >> > >> > Ohh, I have missed that part. Now when re-reading I can see the reason >> > for the perf improvement. It is most likely the higher order free which >> > ends up being much cheaper. This part makes some sense. >> > >> > How much is this feasible is another question. Do not forget we have >> > those external providers of the online callback and those would need to >> > be updated as well. >> Sure Michal, I ll look into this. >> >> > >> > Btw. the normal memmap init code path does the same per-page free as >> > well. If we really want to speed the hotplug path then I guess the init >> > one would see a bigger improvement and those two should be in sync. >> Thanks for pointers, Will look further. > > I haven't looked closer and I will be travelling next week so just > hint. > Have a look at the nobootmem and how it frees pages to the page > allocator in __free_pages_boot_core. Seems exactly what you want and it > also answers your question about reference counting. Thanks Michal. Will send a new version after testing. Regards, Arun