From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f200.google.com (mail-pf0-f200.google.com [209.85.192.200]) by kanga.kvack.org (Postfix) with ESMTP id 1F09C6B0006 for ; Fri, 6 Apr 2018 10:23:45 -0400 (EDT) Received: by mail-pf0-f200.google.com with SMTP id k2so735293pfi.23 for ; Fri, 06 Apr 2018 07:23:45 -0700 (PDT) Received: from mga18.intel.com (mga18.intel.com. [134.134.136.126]) by mx.google.com with ESMTPS id t14si4461193pfg.225.2018.04.06.07.23.43 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 06 Apr 2018 07:23:44 -0700 (PDT) Subject: Re: [PATCH v3 2/4] mm/sparsemem: Defer the ms->section_mem_map clearing References: <20180228032657.32385-1-bhe@redhat.com> <20180228032657.32385-3-bhe@redhat.com> From: Dave Hansen Message-ID: <8e147320-50f5-f809-31d2-992c35ecc418@intel.com> Date: Fri, 6 Apr 2018 07:23:42 -0700 MIME-Version: 1.0 In-Reply-To: <20180228032657.32385-3-bhe@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Baoquan He , linux-kernel@vger.kernel.org, akpm@linux-foundation.org, pagupta@redhat.com Cc: linux-mm@kvack.org, kirill.shutemov@linux.intel.com 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.