On Thu, Aug 23, 2018 at 05:15:39PM -0700, Dave Hansen wrote:

On 08/23/2018 06:07 AM, Wei Yang wrote:

quoted

And it is known, __highest_present_section_nr is a more strict boundary
than NR_MEM_SECTIONS.

What is the benefit of this patch?

The original idea is simple: with a more strict boundary, it will has less
computation.

You're adding a more "strict" boundary, but you're also adding a
potential cacheline miss and removing optimizations that the compiler
can make with a constant vs. a variable.  Providing absolute bounds
limits that the compiler knows about can actually be pretty handy for it
to optimize things

You are right.

I haven't thought about the compiler optimization case.

Do you have *any* analysis to show that this has a benefit?  What does
it do to text size, for instance?

I don't have more analysis about this. Originally, I thought a strict boundary
will have a benefit. But as you mentioned, it loose the compiler optimization.

BTW, I did some tests and found during a normal boot, all the section number
are within NR_MEM_SECTIONS. I am wondering in which case, this check will be
valid and return 0?

-- 
Wei Yang
Help you, Help me