From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail137.messagelabs.com (mail137.messagelabs.com [216.82.249.19]) by kanga.kvack.org (Postfix) with SMTP id 821A76B02A3 for ; Tue, 13 Jul 2010 00:28:03 -0400 (EDT) Received: from m4.gw.fujitsu.co.jp ([10.0.50.74]) by fgwmail6.fujitsu.co.jp (Fujitsu Gateway) with ESMTP id o6D4S1Ra008630 for (envelope-from kamezawa.hiroyu@jp.fujitsu.com); Tue, 13 Jul 2010 13:28:01 +0900 Received: from smail (m4 [127.0.0.1]) by outgoing.m4.gw.fujitsu.co.jp (Postfix) with ESMTP id C1D9145DE6E for ; Tue, 13 Jul 2010 13:28:00 +0900 (JST) Received: from s4.gw.fujitsu.co.jp (s4.gw.fujitsu.co.jp [10.0.50.94]) by m4.gw.fujitsu.co.jp (Postfix) with ESMTP id 95A5A45DE60 for ; Tue, 13 Jul 2010 13:28:00 +0900 (JST) Received: from s4.gw.fujitsu.co.jp (localhost.localdomain [127.0.0.1]) by s4.gw.fujitsu.co.jp (Postfix) with ESMTP id 700A91DB8042 for ; Tue, 13 Jul 2010 13:28:00 +0900 (JST) Received: from m106.s.css.fujitsu.com (m106.s.css.fujitsu.com [10.249.87.106]) by s4.gw.fujitsu.co.jp (Postfix) with ESMTP id 175321DB8037 for ; Tue, 13 Jul 2010 13:27:57 +0900 (JST) Date: Tue, 13 Jul 2010 13:23:12 +0900 From: KAMEZAWA Hiroyuki 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> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org 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 List-ID: 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. > >> A A A section 0 A A A A A A section 1 A A A A A A A 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 { > >> A A A A struct page_cgroup *page_cgroup; > >> A A A A unsigned long pad; > >> A #endif > >> + A A A unsigned long start_pfn; > >> + A A A unsigned long end_pfn; > >> A }; > >> > > > > I have 2 concerns. > > A 1. This makes mem_section twice. Wasting too much memory and not good for cache. > > A A 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. > > A 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, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org