From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753457AbeDPEgS (ORCPT ); Mon, 16 Apr 2018 00:36:18 -0400 Received: from mga12.intel.com ([192.55.52.136]:26369 "EHLO mga12.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751151AbeDPEgR (ORCPT ); Mon, 16 Apr 2018 00:36:17 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.48,458,1517904000"; d="scan'208";a="33923477" Subject: Re: [PATCH v3 4/4] mm/sparse: Optimize memmap allocation during sparse_init() To: Baoquan He References: <20180228032657.32385-1-bhe@redhat.com> <20180228032657.32385-5-bhe@redhat.com> <5dd3942a-cf66-f749-b1c6-217b0c3c94dc@intel.com> <20180408082038.GB19345@localhost.localdomain> <7cc53287-4570-84d6-502c-c3dfbd279b78@intel.com> <20180415021940.GA1750@localhost.localdomain> Cc: linux-kernel@vger.kernel.org, akpm@linux-foundation.org, pagupta@redhat.com, linux-mm@kvack.org, kirill.shutemov@linux.intel.com From: Dave Hansen Message-ID: <11c4796f-865e-9e0c-076a-f750d5da0ea7@intel.com> Date: Sun, 15 Apr 2018 21:36:16 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <20180415021940.GA1750@localhost.localdomain> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/14/2018 07:19 PM, Baoquan He wrote: >>> Yes, this place is the hardest to understand. The temorary arrays are >>> allocated beforehand with the size of 'nr_present_sections'. The error >>> paths you mentioned is caused by allocation failure of mem_map or >>> map_map, but whatever it's error or success paths, the sections must be >>> marked as present in memory_present(). Error or success paths happened >>> in alloc_usemap_and_memmap(), while checking if it's erorr or success >>> paths happened in the last for_each_present_section_nr() of >>> sparse_init(), and clear the ms->section_mem_map if it goes along error >>> paths. This is the key point of this new allocation way. >> I think you owe some commenting because this is so hard to understand. > I can arrange and write a code comment above sparse_init() according to > this patch's git log, do you think it's OK? > > Honestly, it took me several days to write code, while I spent more > than one week to write the patch log. Writing patch log is really a > headache to me. I often find the same: writing the code is the easy part. Explaining why it is right is the hard part.