Re: [PATCH] x86: mm: accurate the comments for STEP_SIZE_SHIFT macro

From: H. Peter Anvin
Date: Mon Mar 18 2013 - 15:17:16 EST

On 03/18/2013 12:13 PM, Yinghai Lu wrote:
>> No, it doesn't. This is C, not elementary school Now I'm really bothered.
>> The comment doesn't say *why* (PUD_SHIFT-PMD_SHIFT)/2 or any other
>> variant is correct, furthermore I suspect that the +1 is misplaced.
>> However, what is really needed is:
>> 1. Someone needs to explain what the logic should be and why, and
>> 2. replace the macro with a symbolic macro, not with a constant and a
>> comment explaining, incorrectly, how that value was derived.
> yes, we should find out free_mem_size instead to decide next step size.
> But that will come out page table size estimation problem again.

Sorry, that comment is double nonsense for someone who isn't intimately
familiar with the code, and it sounds like it is just plain wrong.

Instead, try to explain why 5 is the correct value in the current code
and how it is (or should be!) derived.


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