Messages in this thread | | | Date | Tue, 1 Dec 2015 17:14:32 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH] x86, mtrr: mark range_new in mtrr_calc_range_state() as __initdata |
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* Rasmus Villemoes <linux@rasmusvillemoes.dk> wrote:
> On Fri, Nov 27 2015, Ingo Molnar <mingo@kernel.org> wrote: > > > * Rasmus Villemoes <linux@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 <linux@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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