From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail190.messagelabs.com (mail190.messagelabs.com [216.82.249.51]) by kanga.kvack.org (Postfix) with SMTP id 43BB06B02A3 for ; Tue, 13 Jul 2010 00:11:16 -0400 (EDT) Received: by iwn2 with SMTP id 2so6345226iwn.14 for ; Mon, 12 Jul 2010 21:11:14 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20100713121947.612bd656.kamezawa.hiroyu@jp.fujitsu.com> References: <20100712155348.GA2815@barrios-desktop> <20100713121947.612bd656.kamezawa.hiroyu@jp.fujitsu.com> Date: Tue, 13 Jul 2010 13:11:14 +0900 Message-ID: Subject: Re: [RFC] Tight check of pfn_valid on sparsemem From: Minchan Kim Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org To: KAMEZAWA Hiroyuki 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, 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. >> =A0 =A0 =A0section 0 =A0 =A0 =A0 =A0 =A0 =A0 section 1 =A0 =A0 =A0 =A0 = =A0 =A0 =A0section 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 chec= k. >> It's not what we want. >> >> The Following patch adds check valid pfn range check on pfn_valid of spa= rsemem. >> >> 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 { >> =A0 =A0 =A0 =A0 struct page_cgroup *page_cgroup; >> =A0 =A0 =A0 =A0 unsigned long pad; >> =A0#endif >> + =A0 =A0 =A0 unsigned long start_pfn; >> + =A0 =A0 =A0 unsigned long end_pfn; >> =A0}; >> > > I have 2 concerns. > =A01. This makes mem_section twice. Wasting too much memory and not good = for cache. > =A0 =A0But 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. > =A02. This can't be help for a case where a section has multiple small ho= les. 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. > =3D=3D > 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? --=20 Kind regards, Minchan Kim -- 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