From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751626AbdJCQCw (ORCPT ); Tue, 3 Oct 2017 12:02:52 -0400 Received: from userp1040.oracle.com ([156.151.31.81]:38936 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750787AbdJCQCs (ORCPT ); Tue, 3 Oct 2017 12:02:48 -0400 Subject: Re: [PATCH v9 03/12] mm: deferred_init_memmap improvements From: Pasha Tatashin To: Michal Hocko Cc: linux-kernel@vger.kernel.org, sparclinux@vger.kernel.org, linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-arm-kernel@lists.infradead.org, x86@kernel.org, kasan-dev@googlegroups.com, borntraeger@de.ibm.com, heiko.carstens@de.ibm.com, davem@davemloft.net, willy@infradead.org, ard.biesheuvel@linaro.org, mark.rutland@arm.com, will.deacon@arm.com, catalin.marinas@arm.com, sam@ravnborg.org, mgorman@techsingularity.net, steven.sistare@oracle.com, daniel.m.jordan@oracle.com, bob.picco@oracle.com References: <20170920201714.19817-1-pasha.tatashin@oracle.com> <20170920201714.19817-4-pasha.tatashin@oracle.com> <20171003125754.2kuqzkstywg7axhd@dhcp22.suse.cz> Message-ID: Date: Tue, 3 Oct 2017 12:01:08 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.3.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Source-IP: aserv0022.oracle.com [141.146.126.234] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Michal, Are you OK, if I replace DEFERRED_FREE() macro with a function like this: /* * Helper for deferred_init_range, free the given range, and reset the * counters */ static inline unsigned long __def_free(unsigned long *nr_free, unsigned long *free_base_pfn, struct page **page) { unsigned long nr = *nr_free; deferred_free_range(*free_base_pfn, nr); *free_base_pfn = 0; *nr_free = 0; *page = NULL; return nr; } Since it is inline, and we operate with non-volatile counters, compiler will be smart enough to remove all the unnecessary de-references. As a plus, we won't be adding any new branches, and the code is still going to stay compact. Pasha On 10/03/2017 11:15 AM, Pasha Tatashin wrote: > Hi Michal, > >> >> Please be explicit that this is possible only because we discard >> memblock data later after 3010f876500f ("mm: discard memblock data >> later"). Also be more explicit how the new code works. > > OK > >> >> I like how the resulting code is more compact and smaller. > > That was the goal :) > >> for_each_free_mem_range also looks more appropriate but I really detest >> the DEFERRED_FREE thingy. Maybe we can handle all that in a single goto >> section. I know this is not an art but manipulating variables from >> macros is more error prone and much more ugly IMHO. > > Sure, I can re-arrange to have a goto place. Function won't be as small, > and if compiler is not smart enough we might end up with having more > branches than what my current code has. > >> >> please do not use macros. Btw. this deserves its own fix. I suspect that >> no CONFIG_HOLES_IN_ZONE arch enables DEFERRED_STRUCT_PAGE_INIT but >> purely from the review point of view it should be its own patch. > > Sure, I will submit this patch separately from the rest of the project. > In my opinion DEFERRED_STRUCT_PAGE_INIT is the way of the future, so we > should make sure it is working with as many configs as possible. > > Thank you, > Pasha