From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f70.google.com (mail-ed1-f70.google.com [209.85.208.70]) by kanga.kvack.org (Postfix) with ESMTP id 08C546B0008 for ; Thu, 19 Jul 2018 11:16:00 -0400 (EDT) Received: by mail-ed1-f70.google.com with SMTP id s18-v6so3420411edr.15 for ; Thu, 19 Jul 2018 08:15:59 -0700 (PDT) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id 3-v6si1199914edc.284.2018.07.19.08.15.58 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 19 Jul 2018 08:15:58 -0700 (PDT) Date: Thu, 19 Jul 2018 17:15:55 +0200 From: Michal Hocko Subject: Re: [PATCH v2 3/5] mm/page_alloc: Optimize free_area_init_core Message-ID: <20180719151555.GH7193@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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180719140327.GB10988@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 Thu 19-07-18 16:03:27, Oscar Salvador wrote: > On Thu, Jul 19, 2018 at 03:44:17PM +0200, Michal Hocko wrote: > > On Thu 19-07-18 15:27:38, osalvador@techadventures.net wrote: > > > From: Oscar Salvador > > > > > > In free_area_init_core we calculate the amount of managed pages > > > we are left with, by substracting the memmap pages and the pages > > > reserved for dma. > > > With the values left, we also account the total of kernel pages and > > > the total of pages. > > > > > > Since memmap pages are calculated from zone->spanned_pages, > > > let us only do these calculcations whenever zone->spanned_pages is greather > > > than 0. > > > > But why do we care? How do we test this? In other words, why is this > > worth merging? > > Uhm, unless the values are going to be updated, why do we want to go through all > comparasions/checks? > I thought it was a nice thing to have the chance to skip that block unless we are going to > update the counters. > > Again, if you think this only adds complexity and no good, I can drop it. Your changelog doesn't really explain the motivation. Does the change help performance? Is this a pure cleanup? 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. Btw. are you sure this change is correct? E.g. /* * Set an approximate value for lowmem here, it will be adjusted * when the bootmem allocator frees pages into the buddy system. * And all highmem pages will be managed by the buddy system. */ zone->managed_pages = is_highmem_idx(j) ? realsize : freesize; expects freesize to be calculated properly and just from quick reading the code I do not see why skipping other adjustments is ok for size > 0. Maybe this is OK, I dunno and my brain is already heading few days off but a real cleanup wouldn't even make me think what the heck is going on here. -- Michal Hocko SUSE Labs