Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751541Ab0GME2E (ORCPT ); Tue, 13 Jul 2010 00:28:04 -0400 Received: from fgwmail6.fujitsu.co.jp ([192.51.44.36]:36528 "EHLO fgwmail6.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750830Ab0GME2A (ORCPT ); Tue, 13 Jul 2010 00:28:00 -0400 X-SecurityPolicyCheck-FJ: OK by FujitsuOutboundMailChecker v1.3.1 Date: Tue, 13 Jul 2010 13:23:12 +0900 From: KAMEZAWA Hiroyuki To: Minchan Kim Cc: linux@arm.linux.org.uk, Yinghai Lu , "H. Peter Anvin" , Andrew Morton , Shaohua Li , Yakui Zhao , linux-kernel@vger.kernel.org, linux-mm@kvack.org, arm-kernel@lists.infradead.org, kgene.kim@samsung.com, Mel Gorman Subject: Re: [RFC] Tight check of pfn_valid on sparsemem Message-Id: <20100713132312.a7dfb100.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: References: <20100712155348.GA2815@barrios-desktop> <20100713121947.612bd656.kamezawa.hiroyu@jp.fujitsu.com> Organization: FUJITSU Co. LTD. X-Mailer: Sylpheed 3.0.3 (GTK+ 2.10.14; i686-pc-mingw32) Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3245 Lines: 89 On Tue, 13 Jul 2010 13:11:14 +0900 Minchan Kim wrote: > On Tue, Jul 13, 2010 at 12:19 PM, KAMEZAWA Hiroyuki > wrote: > > On Tue, 13 Jul 2010 00:53:48 +0900 > > Minchan Kim wrote: > > > >> Kukjin, Could you test below patch? > >> I don't have any sparsemem system. Sorry. > >> > >> -- CUT DOWN HERE -- > >> > >> Kukjin reported oops happen while he change min_free_kbytes > >> http://www.spinics.net/lists/arm-kernel/msg92894.html > >> It happen by memory map on sparsemem. > >> > >> The system has a memory map following as. > >>      section 0             section 1              section 2 > >> 0x20000000-0x25000000, 0x40000000-0x50000000, 0x50000000-0x58000000 > >> SECTION_SIZE_BITS 28(256M) > >> > >> It means section 0 is an incompletely filled section. > >> Nontheless, current pfn_valid of sparsemem checks pfn loosely. > >> > >> It checks only mem_section's validation. > >> So in above case, pfn on 0x25000000 can pass pfn_valid's validation check. > >> It's not what we want. > >> > >> The Following patch adds check valid pfn range check on pfn_valid of sparsemem. > >> > >> Signed-off-by: Minchan Kim > >> Reported-by: Kukjin Kim > >> > >> P.S) > >> It is just RFC. If we agree with this, I will make the patch on mmotm. > >> > >> -- > >> > >> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > >> index b4d109e..6c2147a 100644 > >> --- a/include/linux/mmzone.h > >> +++ b/include/linux/mmzone.h > >> @@ -979,6 +979,8 @@ struct mem_section { > >>         struct page_cgroup *page_cgroup; > >>         unsigned long pad; > >>  #endif > >> +       unsigned long start_pfn; > >> +       unsigned long end_pfn; > >>  }; > >> > > > > I have 2 concerns. > >  1. This makes mem_section twice. Wasting too much memory and not good for cache. > >    But yes, you can put this under some CONFIG which has small number of mem_section[]. > > > > I think memory usage isn't a big deal. but for cache, we can move > fields into just after section_mem_map. > I don't think so. This addtional field can eat up the amount of memory you saved by unmap. > >  2. This can't be help for a case where a section has multiple small holes. > > I agree. But this(not punched hole but not filled section problem) > isn't such case. But it would be better to handle it altogether. :) > > > > > Then, my proposal for HOLES_IN_MEMMAP sparsemem is below. > > == > > Some architectures unmap memmap[] for memory holes even with SPARSEMEM. > > To handle that, pfn_valid() should check there are really memmap or not. > > For that purpose, __get_user() can be used. > > Look at free_unused_memmap. We don't unmap pte of hole memmap. > Is __get_use effective, still? > __get_user() works with TLB and page table, the vaddr is really mapped or not. If you got SEGV, __get_user() returns -EFAULT. It works per page granule. Thanks, -Kame -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/