From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f71.google.com (mail-ed1-f71.google.com [209.85.208.71]) by kanga.kvack.org (Postfix) with ESMTP id 4DABA6B0008 for ; Mon, 23 Jul 2018 04:35:21 -0400 (EDT) Received: by mail-ed1-f71.google.com with SMTP id d18-v6so131401edp.0 for ; Mon, 23 Jul 2018 01:35:21 -0700 (PDT) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id r23-v6si7428385edi.91.2018.07.23.01.35.20 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 23 Jul 2018 01:35:20 -0700 (PDT) Date: Mon, 23 Jul 2018 10:35:19 +0200 From: Michal Hocko Subject: Re: [PATCH v2 3/5] mm/page_alloc: Optimize free_area_init_core Message-ID: <20180723083519.GG17905@dhcp22.suse.cz> References: <20180719132740.32743-1-osalvador@techadventures.net> <20180719132740.32743-4-osalvador@techadventures.net> <20180719134417.GC7193@dhcp22.suse.cz> <20180719140327.GB10988@techadventures.net> <20180719151555.GH7193@dhcp22.suse.cz> <20180719205235.GA14010@techadventures.net> <20180720100327.GA19478@techadventures.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180720100327.GA19478@techadventures.net> Sender: owner-linux-mm@kvack.org List-ID: To: Oscar Salvador Cc: akpm@linux-foundation.org, pasha.tatashin@oracle.com, vbabka@suse.cz, aaron.lu@intel.com, iamjoonsoo.kim@lge.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Oscar Salvador On Fri 20-07-18 12:03:27, Oscar Salvador wrote: > On Thu, Jul 19, 2018 at 10:52:35PM +0200, Oscar Salvador wrote: > > On Thu, Jul 19, 2018 at 05:15:55PM +0200, Michal Hocko wrote: > > > Your changelog doesn't really explain the motivation. Does the change > > > help performance? Is this a pure cleanup? > > > > Hi Michal, > > > > Sorry to not have explained this better from the very beginning. > > > > It should help a bit in performance terms as we would be skipping those > > condition checks and assignations for zones that do not have any pages. > > It is not a huge win, but I think that skipping code we do not really need to run > > is worh to have. > > > > > The function is certainly not an example of beauty. It is more an > > > example of changes done on top of older ones without much thinking. But > > > I do not see your change would make it so much better. I would consider > > > it a much nicer cleanup if it was split into logical units each doing > > > one specific thing. > > > > About the cleanup, I thought that moving that block of code to a separate function > > would make the code easier to follow. > > If you think that this is still not enough, I can try to split it and see the outcome. > > I tried to split it innto three logical blocks: > > - Substract memmap pages > - Substract dma reserves > - Account kernel pages (nr_kernel_pages and nr_total_pages) No, I do not think this is much better. Why do we need to separate those functions out? I think you are too focused on the current function without a broader context. Think about it. We have two code paths. Early initialization and the hotplug. The two are subtly different in some aspects. Maybe reusing free_area_init_core is the wrong thing and we should have a dedicated subset of this function. This would make the code more clear probably. You wouldn't have to think which part of free_area_init_core is special and what has to be done if this function was to be used in a different context. See my point? -- Michal Hocko SUSE Labs