From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751557AbeDHGvE (ORCPT ); Sun, 8 Apr 2018 02:51:04 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:44020 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750924AbeDHGvD (ORCPT ); Sun, 8 Apr 2018 02:51:03 -0400 Date: Sun, 8 Apr 2018 14:50:55 +0800 From: Baoquan He To: Dave Hansen Cc: linux-kernel@vger.kernel.org, akpm@linux-foundation.org, pagupta@redhat.com, linux-mm@kvack.org, kirill.shutemov@linux.intel.com Subject: Re: [PATCH v3 2/4] mm/sparsemem: Defer the ms->section_mem_map clearing Message-ID: <20180408065055.GA19345@localhost.localdomain> References: <20180228032657.32385-1-bhe@redhat.com> <20180228032657.32385-3-bhe@redhat.com> <8e147320-50f5-f809-31d2-992c35ecc418@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <8e147320-50f5-f809-31d2-992c35ecc418@intel.com> User-Agent: Mutt/1.9.1 (2017-09-22) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Dave, Thanks a lot for your careful reviewing! On 04/06/18 at 07:23am, Dave Hansen wrote: > On 02/27/2018 07:26 PM, Baoquan He wrote: > > In sparse_init(), if CONFIG_SPARSEMEM_ALLOC_MEM_MAP_TOGETHER=y, system > > will allocate one continuous memory chunk for mem maps on one node and > > populate the relevant page tables to map memory section one by one. If > > fail to populate for a certain mem section, print warning and its > > ->section_mem_map will be cleared to cancel the marking of being present. > > Like this, the number of mem sections marked as present could become > > less during sparse_init() execution. > > > > Here just defer the ms->section_mem_map clearing if failed to populate > > its page tables until the last for_each_present_section_nr() loop. This > > is in preparation for later optimizing the mem map allocation. > > > > Signed-off-by: Baoquan He > > --- > > mm/sparse-vmemmap.c | 1 - > > mm/sparse.c | 12 ++++++++---- > > 2 files changed, 8 insertions(+), 5 deletions(-) > > > > diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c > > index bd0276d5f66b..640e68f8324b 100644 > > --- a/mm/sparse-vmemmap.c > > +++ b/mm/sparse-vmemmap.c > > @@ -303,7 +303,6 @@ void __init sparse_mem_maps_populate_node(struct page **map_map, > > ms = __nr_to_section(pnum); > > pr_err("%s: sparsemem memory map backing failed some memory will not be available\n", > > __func__); > > - ms->section_mem_map = 0; > > } > > I think you might have been trying to say this in the description, but I > was not able to parse it out of there. What is in ms->section_mem_map > that needs to get cleared? > > It *looks* like memory_present() uses ms->section_mem_map to just mark > which sections are online relatively early in boot. We need this > clearing to mark that they are effectively *not* present any longer. > Correct? > > I guess the concern here is that if you miss any of the error sites, > we'll end up with a bogus, non-null ms->section_mem_map. Do we handle > that nicely? > > Should the " = 0" instead be clearing SECTION_MARKED_PRESENT or > something? That would make it easier to match the code up with the code > that it is effectively undoing. Not sure if I understand your question correctly. From memory_present(), information encoded into ms->section_mem_map including numa node, SECTION_IS_ONLINE and SECTION_MARKED_PRESENT. Not sure if it's OK to only clear SECTION_MARKED_PRESENT. People may wrongly check SECTION_IS_ONLINE and do something on this memory section? Thanks Baoquan