From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f199.google.com (mail-wr0-f199.google.com [209.85.128.199]) by kanga.kvack.org (Postfix) with ESMTP id E4A016B0592 for ; Wed, 9 May 2018 17:09:22 -0400 (EDT) Received: by mail-wr0-f199.google.com with SMTP id g7-v6so24824747wrb.19 for ; Wed, 09 May 2018 14:09:22 -0700 (PDT) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id s14-v6si2765389eds.258.2018.05.09.14.09.21 for (version=TLS1 cipher=AES128-SHA bits=128/128); Wed, 09 May 2018 14:09:21 -0700 (PDT) Date: Wed, 9 May 2018 23:09:20 +0200 From: Michal Hocko Subject: Re: [PATCH] mm: allow deferred page init for vmemmap only Message-ID: <20180509210920.GZ32366@dhcp22.suse.cz> References: <20180509191713.23794-1-pasha.tatashin@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180509191713.23794-1-pasha.tatashin@oracle.com> Sender: owner-linux-mm@kvack.org List-ID: To: Pavel Tatashin Cc: steven.sistare@oracle.com, daniel.m.jordan@oracle.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, tglx@linutronix.de, linux-mm@kvack.org, mgorman@techsingularity.net, mingo@kernel.org, peterz@infradead.org, rostedt@goodmis.org, fengguang.wu@intel.com, dennisszhou@gmail.com On Wed 09-05-18 15:17:13, Pavel Tatashin wrote: > It is unsafe to do virtual to physical translations before mm_init() is > called if struct page is needed in order to determine the memory section > number (see SECTION_IN_PAGE_FLAGS). This is because only in mm_init() we > initialize struct pages for all the allocated memory when deferred struct > pages are used. > > My recent fix exposed this problem, because it greatly reduced number of > pages that are initialized before mm_init(), but the problem existed even > before my fix, as Fengguang Wu found. > > Since FLATMEM is already disallowed for deferred struct pages, it makes > sense to allow deferred struct pages only on systems with > SPARSEMEM_VMEMMAP. This doesn't really explain why CONFIG_SPARSMEM or DISCONTIG has the problem. > The problems are discussed in these threads: > http://lkml.kernel.org/r/20180418135300.inazvpxjxowogyge@wfg-t540p.sh.intel.com > http://lkml.kernel.org/r/20180419013128.iurzouiqxvcnpbvz@wfg-t540p.sh.intel.com > http://lkml.kernel.org/r/20180426202619.2768-1-pasha.tatashin@oracle.com Using references is good but there should be a highlevel summary in the chaneglog as well. > Fixes: 3a80a7fa7989 ("mm: meminit: initialise a subset of struct pages if CONFIG_DEFERRED_STRUCT_PAGE_INIT is set") > Signed-off-by: Pavel Tatashin > --- > mm/Kconfig | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/Kconfig b/mm/Kconfig > index d5004d82a1d6..1cd32d67ca30 100644 > --- a/mm/Kconfig > +++ b/mm/Kconfig > @@ -635,7 +635,7 @@ config DEFERRED_STRUCT_PAGE_INIT > bool "Defer initialisation of struct pages to kthreads" > default n > depends on NO_BOOTMEM > - depends on !FLATMEM > + depends on SPARSEMEM_VMEMMAP > help > Ordinarily all struct pages are initialised during early boot in a > single thread. On very large machines this can take a considerable > -- > 2.17.0 > -- Michal Hocko SUSE Labs