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=-2.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 342EEC4BA12 for ; Wed, 26 Feb 2020 12:30:45 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id CED8724684 for ; Wed, 26 Feb 2020 12:30:44 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="RWRHua45" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CED8724684 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 3BCC86B0003; Wed, 26 Feb 2020 07:30:44 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 36CEE6B0005; Wed, 26 Feb 2020 07:30:44 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 2AB126B0006; Wed, 26 Feb 2020 07:30:44 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0061.hostedemail.com [216.40.44.61]) by kanga.kvack.org (Postfix) with ESMTP id 136366B0003 for ; Wed, 26 Feb 2020 07:30:44 -0500 (EST) Received: from smtpin17.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 9695E181AC9C6 for ; Wed, 26 Feb 2020 12:30:43 +0000 (UTC) X-FDA: 76532211966.17.book51_2362877f54e0a X-HE-Tag: book51_2362877f54e0a X-Filterd-Recvd-Size: 5679 Received: from us-smtp-1.mimecast.com (us-smtp-delivery-1.mimecast.com [207.211.31.120]) by imf50.hostedemail.com (Postfix) with ESMTP for ; Wed, 26 Feb 2020 12:30:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1582720242; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=USc4GZx7VeByANQXh3m8ONczXPb4tD0GznPgTK+y2dM=; b=RWRHua45/+GMj/Gcv7raJZzg9N2ToVdDtjmTfU2DTMn6bMaLYBO53UXHWZvM6bsiFtmYXr TkZzutg2lTjZnMj+BB0EGDslGRPi55oVQMizn36K2Bgc1PtS1tk5i5kuqObJVRWA53BVR6 qJwRZZs0PSQMy7t/KrDKscIdzJgbZ5Q= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-115-SqhY_Z7XMm61uUtse-5Haw-1; Wed, 26 Feb 2020 07:30:38 -0500 X-MC-Unique: SqhY_Z7XMm61uUtse-5Haw-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id AD166107ACC7; Wed, 26 Feb 2020 12:30:36 +0000 (UTC) Received: from localhost (ovpn-12-39.pek2.redhat.com [10.72.12.39]) by smtp.corp.redhat.com (Postfix) with ESMTPS id BAA8F5DA60; Wed, 26 Feb 2020 12:30:32 +0000 (UTC) Date: Wed, 26 Feb 2020 20:30:30 +0800 From: Baoquan He To: Michal Hocko Cc: David Hildenbrand , linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, richardw.yang@linux.intel.com, osalvador@suse.de, dan.j.williams@intel.com, rppt@linux.ibm.com, robin.murphy@arm.com Subject: Re: [PATCH v2 0/7] mm/hotplug: Only use subsection map in VMEMMAP case Message-ID: <20200226123030.GG24216@MiWiFi-R3L-srv> References: <20200220043316.19668-1-bhe@redhat.com> <20200220103849.GG20509@dhcp22.suse.cz> <20200221142847.GG4937@MiWiFi-R3L-srv> <75b4f840-7454-d6d0-5453-f0a045c852fa@redhat.com> <20200225100226.GM22443@dhcp22.suse.cz> <20200226034236.GD24216@MiWiFi-R3L-srv> <20200226091421.GE3771@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200226091421.GE3771@dhcp22.suse.cz> User-Agent: Mutt/1.10.1 (2018-07-13) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 02/26/20 at 10:14am, Michal Hocko wrote: > On Wed 26-02-20 11:42:36, Baoquan He wrote: > > On 02/25/20 at 11:02am, Michal Hocko wrote: > > > On Tue 25-02-20 10:10:45, David Hildenbrand wrote: > > > > >>> include/linux/mmzone.h | 2 + > > > > >>> mm/sparse.c | 178 +++++++++++++++++++++++++++++------------ > > > > >>> 2 files changed, 127 insertions(+), 53 deletions(-) > > > > >> > > > > >> Why do we need to add so much code to remove a functionality from one > > > > >> memory model? > > > > > > > > > > Hmm, Dan also asked this before. > > > > > > > > > > The adding mainly happens in patch 2, 3, 4, including the two newly > > > > > added function defitions, the code comments above them, and those added > > > > > dummy functions for !VMEMMAP. > > > > > > > > AFAIKS, it's mostly a bunch of newly added comments on top of functions. > > > > E.g., the comment for fill_subsection_map() alone spans 12 LOC in total. > > > > I do wonder if we have to be that verbose. We are barely that verbose on > > > > MM code (and usually I don't see much benefit unless it's a function > > > > with many users from many different places). > > > > > > I would tend to agree here. Not that I am against kernel doc > > > documentation but these are internal functions and the comment doesn't > > > really give any better insight IMHO. I would be much more inclined if > > > this was the general pattern in the respective file but it just stands > > > out. > > > > I saw there are internal functions which have code comments, e.g > > shrink_slab() in mm/vmscan.c, not only this one place, there are several > > places. I personally prefer to see code comment for function if > > possible, this can save time, e.g people can skip the bitmap operation > > when read code if not necessary. And here I mainly want to tell there > > are different returned value to note different behaviour when call them. > > ... yet nobody really cares about different return code. It is an error > that is propagated up the call chain and that's all. > > I also like when there is a kernel doc comment that helps to understand > the intented usage, context the function can be called from, potential > side effects, locking requirements and other details people need to know Fair enough. As I have said, I didn't intend to stick to add kernel doc comments for these two functions. Will remove them. Thanks for reviewing. > when calling functions. But have a look at > /** > * clear_subsection_map - Clear subsection map of one memory region > * > * @pfn - start pfn of the memory range > * @nr_pages - number of pfns to add in the region > * > * This is only intended for hotplug, and clear the related subsection > * map inside one section. > * > * Return: > * * -EINVAL - Section already deactived. > * * 0 - Subsection map is emptied. > * * 1 - Subsection map is not empty. > */ > > the only useful information in here is that this is a hotplug stuff but > I would be completely lost about the intention without already knowing > what is this whole subsection about. > > -- > Michal Hocko > SUSE Labs >