From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail138.messagelabs.com (mail138.messagelabs.com [216.82.249.35]) by kanga.kvack.org (Postfix) with SMTP id E4A466B029C for ; Wed, 5 May 2010 21:24:07 -0400 (EDT) Received: by vws3 with SMTP id 3so1636997vws.14 for ; Wed, 05 May 2010 18:24:06 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <4BE14335.10702@ru.mvista.com> References: <20100420155122.6f2c26eb.akpm@linux-foundation.org> <20100420230719.GB1432@n2100.arm.linux.org.uk> <4BE14335.10702@ru.mvista.com> Date: Thu, 6 May 2010 10:24:06 +0900 Message-ID: Subject: Re: Suspicious compilation warning From: Kyungmin Park Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org To: Sergei Shtylyov Cc: Russell King - ARM Linux , Stephen Rothwell , Marcelo Jimenez , Christoph Lameter , Mel Gorman , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Minchan Kim , KOSAKI Motohiro , "H. Peter Anvin" , Andrew Morton , Yinghai Lu , linux-arm-kernel@lists.infradead.org List-ID: On Wed, May 5, 2010 at 7:06 PM, Sergei Shtylyov wrot= e: > Hello. > > Russell King - ARM Linux wrote: > >>>> I get this warning while compiling for ARM/SA1100: >>>> >>>> mm/sparse.c: In function '__section_nr': >>>> mm/sparse.c:135: warning: 'root' is used uninitialized in this functio= n >>>> >>>> With a small patch in fs/proc/meminfo.c, I find that NR_SECTION_ROOTS >>>> is zero, which certainly explains the warning. >>>> >>>> # cat /proc/meminfo >>>> NR_SECTION_ROOTS=3D0 >>>> NR_MEM_SECTIONS=3D32 >>>> SECTIONS_PER_ROOT=3D512 >>>> SECTIONS_SHIFT=3D5 >>>> MAX_PHYSMEM_BITS=3D32 >>>> >>> >>> hm, who owns sparsemem nowadays? Nobody identifiable. >>> >>> Does it make physical sense to have SECTIONS_PER_ROOT > NR_MEM_SECTIONS= ? >>> >> >> Well, it'll be about this number on everything using sparsemem extreme: >> >> #define SECTIONS_PER_ROOT =A0 =A0 =A0 (PAGE_SIZE / sizeof (struct mem_se= ction)) >> >> and with only 32 sections, this is going to give a NR_SECTION_ROOTS valu= e >> of zero. =A0I think the calculation of NR_SECTIONS_ROOTS is wrong. >> >> #define NR_SECTION_ROOTS =A0 =A0 =A0 =A0(NR_MEM_SECTIONS / SECTIONS_PER_= ROOT) >> >> Clearly if we have 1 mem section, we want to have one section root, so >> I think this division should round up any fractional part, thusly: >> >> #define NR_SECTION_ROOTS =A0 =A0 =A0 =A0((NR_MEM_SECTIONS + SECTIONS_PER= _ROOT - 1) >> / SECTIONS_PER_ROOT) >> > > =A0There's DIV_ROUND_UP() macro for this kind of calculation. Hi, It tested with my board and working. Just curious. If NR_SECTION_ROOTS is zero and uninitialized then what's problem? Since we boot and working without patch. Thank you, Kyungmin Park -- 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