* Rasmus Villemoes <li...@rasmusvillemoes.dk> wrote:
> On Fri, Nov 27 2015, Ingo Molnar <mi...@kernel.org> wrote:
>
> > * Rasmus Villemoes <li...@rasmusvillemoes.dk> wrote:
> >
> >> range_new doesn't seem to be used after init. It is only passed to
> >> memset, sum_ranges, memcmp and x86_get_mtrr_mem_range, the latter of
> >> which also only passes it on to various *range* library functions. So
> >> mark it __initdata to free up an extra page after init.
> >>
> >> nr_range_new is unconditionally assigned to before it is read, so
> >> there's no point in having it static.
> >>
> >> Signed-off-by: Rasmus Villemoes <li...@rasmusvillemoes.dk>
> >> ---
> >> arch/x86/kernel/cpu/mtrr/cleanup.c | 4 ++--
> >> 1 file changed, 2 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/arch/x86/kernel/cpu/mtrr/cleanup.c
> >> b/arch/x86/kernel/cpu/mtrr/cleanup.c
> >> index 70d7c93f4550..b1a9ad366f67 100644
> >> --- a/arch/x86/kernel/cpu/mtrr/cleanup.c
> >> +++ b/arch/x86/kernel/cpu/mtrr/cleanup.c
> >> @@ -593,9 +593,9 @@ mtrr_calc_range_state(u64 chunk_size, u64 gran_size,
> >> unsigned long x_remove_base,
> >> unsigned long x_remove_size, int i)
> >> {
> >> - static struct range range_new[RANGE_NUM];
> >> + static struct range range_new[RANGE_NUM] __initdata;
> >> unsigned long range_sums_new;
> >> - static int nr_range_new;
> >> + int nr_range_new;
> >> int num_reg;
> >>
> >> /* Convert ranges to var ranges state: */
> >
> > So this static variable actually surprised me - I never realized it was
> > there -
> > and it's not some simple 'once' flag, but something that is essential
> > semantics.
> >
> > So marking it __initdata is correct, but please also move it out of
> > function local
> > variables scope, into file scope - and name it properly as well, like
> > mtrr_new_range[] or so?
>
> I can certainly do that, but isn't the usual preference to keep the scope as
> small as possible? IOW, why do you want to make this a file-scoped variable?
The preference is to keep code readable and obvious, and this one wasn't:
relevant
state/data was hidden via a non-commented local static variable.
> Also, I don't really see how the 'static' has 'essential semantics'. AFAICT,
> the
> contents are wiped on every invocation of mtrr_calc_range_state, so the only
> reason it's static is to avoid blowing the stack.
So this was another property that wasn't obvious from the limited context I saw
in
the patch, i.e. the variable definition. Another solution would be to add a
comment explaining that this is a local variable to keep kernel stack size
down,
and explain why it's safe to do that.
Thanks,
Ingo
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