Re: Suspicious compilation warning

[Sergei Shtylyov]

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.

WBR, Sergei

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