From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935542AbdGTNll (ORCPT ); Thu, 20 Jul 2017 09:41:41 -0400 Received: from mx2.suse.de ([195.135.220.15]:41971 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S934130AbdGTNkl (ORCPT ); Thu, 20 Jul 2017 09:40:41 -0400 From: Vlastimil Babka To: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, Joonsoo Kim , Andrew Morton , Michal Hocko , Mel Gorman , Yang Shi , Laura Abbott , Vinayak Menon , zhong jiang , Vlastimil Babka Subject: [RFC PATCH 4/4] mm, page_ext: move page_ext_init() after page_alloc_init_late() Date: Thu, 20 Jul 2017 15:40:29 +0200 Message-Id: <20170720134029.25268-5-vbabka@suse.cz> X-Mailer: git-send-email 2.13.2 In-Reply-To: <20170720134029.25268-1-vbabka@suse.cz> References: <20170720134029.25268-1-vbabka@suse.cz> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit b8f1a75d61d8 ("mm: call page_ext_init() after all struct pages are initialized") has avoided a a NULL pointer dereference due to DEFERRED_STRUCT_PAGE_INIT clashing with page_ext, by calling page_ext_init() only after the deferred struct page init has finished. Later commit fe53ca54270a ("mm: use early_pfn_to_nid in page_ext_init") avoided the underlying issue differently and moved the page_ext_init() call back to where it was before. However, there are two problems with the current code: - on very large machines, page_ext_init() may fail to allocate the page_ext structures, because deferred struct page init hasn't yet started, and the pre-inited part might be too small. This has been observed with a 3TB machine with page_owner=on. Although it was an older kernel where page_owner hasn't yet been converted to stack depot, thus page_ext was larger, the fundamental problem is still in mainline. - page_owner's init_pages_in_zone() is called before deferred struct page init has started, so it will encounter unitialized struct pages. This currently happens to cause no harm, because the memmap array is are pre-zeroed on allocation and thus the "if (page_zone(page) != zone)" check is negative, but that pre-zeroing guarantee might change soon. The second problem could be also solved by limiting init_page_in_zone() by pgdat->first_deferred_pfn, but fixing the first issue would be more problematic. So this patch again moves page_ext_init() to wait for deferred struct page init to finish. This has some performance implications for boot time, which should be acceptable when enabling debugging functionality. We however keep the benefits of parallel initialization (one kthread per node) so it's better than e.g. disabling DEFERRED_STRUCT_PAGE_INIT completely when page_ext is being used. This effectively reverts commit fe53ca54270a757f0a28ee6bf3a54d952b550ed0. Signed-off-by: Vlastimil Babka --- init/main.c | 3 ++- mm/page_ext.c | 4 +--- 2 files changed, 3 insertions(+), 4 deletions(-) diff --git a/init/main.c b/init/main.c index f866510472d7..7b6517fe0980 100644 --- a/init/main.c +++ b/init/main.c @@ -628,7 +628,6 @@ asmlinkage __visible void __init start_kernel(void) initrd_start = 0; } #endif - page_ext_init(); debug_objects_mem_init(); kmemleak_init(); setup_per_cpu_pageset(); @@ -1035,6 +1034,8 @@ static noinline void __init kernel_init_freeable(void) sched_init_smp(); page_alloc_init_late(); + /* Initialize page ext after all struct pages are initializaed */ + page_ext_init(); do_basic_setup(); diff --git a/mm/page_ext.c b/mm/page_ext.c index 24cf8abefc8d..8522ebd784ac 100644 --- a/mm/page_ext.c +++ b/mm/page_ext.c @@ -402,10 +402,8 @@ void __init page_ext_init(void) * We know some arch can have a nodes layout such as * -------------pfn--------------> * N0 | N1 | N2 | N0 | N1 | N2|.... - * - * Take into account DEFERRED_STRUCT_PAGE_INIT. */ - if (early_pfn_to_nid(pfn) != nid) + if (pfn_to_nid(pfn) != nid) continue; if (init_section_page_ext(pfn, nid)) goto oom; -- 2.13.2