From mboxrd@z Thu Jan 1 00:00:00 1970 From: kmpark@infradead.org (Kyungmin Park) Date: Thu, 6 May 2010 10:24:06 +0900 Subject: Suspicious compilation warning 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> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Wed, May 5, 2010 at 7:06 PM, Sergei Shtylyov wrote: > 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 function >>>> >>>> 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=0 >>>> NR_MEM_SECTIONS=32 >>>> SECTIONS_PER_ROOT=512 >>>> SECTIONS_SHIFT=5 >>>> MAX_PHYSMEM_BITS=32 >>>> >>> >>> 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 ? ? ? (PAGE_SIZE / sizeof (struct mem_section)) >> >> and with only 32 sections, this is going to give a NR_SECTION_ROOTS value >> of zero. ?I think the calculation of NR_SECTIONS_ROOTS is wrong. >> >> #define NR_SECTION_ROOTS ? ? ? ?(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 ? ? ? ?((NR_MEM_SECTIONS + SECTIONS_PER_ROOT - 1) >> / SECTIONS_PER_ROOT) >> > > ?There'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