Re: [External] Re: [PATCH v18 9/9] mm: hugetlb: optimize the code with the help of the compiler

[Oscar Salvador]

On Thu, Mar 11, 2021 at 01:16:37PM +0100, Michal Hocko wrote:
> On Thu 11-03-21 18:00:09, Muchun Song wrote:
> [...]
> > Sorry. I am confused why you disagree with this change.
> > It does not bring any disadvantages.
> 
> Because it is adding a code which is not really necessary and which will
> have to be maintained. Think of future changes which would need to grow
> more of these. Hugetlb code paths shouldn't really think about size of
> the struct page.

I have to confess that when I looked at the patch I found it nice in the way that
wipes out almost all clode dealing with vmemmap when sizeof(struct page) != power_of_2,
and I was convinced by the fact that only two places required the change.
So all in all it did not look like much churn, and not __that__ hard to maintain.

But I did not think in the case where this trick needs to be spread in more places
if the code changes over time.

So I agree that although it gets rid of a lot of code, it would seldomly pay off as
not many configuration out there are running on !power_of_2, and hugetlb is already
tricky enough.


-- 
Oscar Salvador
SUSE L3