Re: [PATCH 4/4] mm,hugetlb: compute page_size_log properly

[Davidlohr Bueso]

On Fri, 10 Feb 2017, Michal Hocko wrote:

> On Thu 09-02-17 12:53:02, Davidlohr Bueso wrote:
> > The SHM_HUGE_* stuff  was introduced in:
> >
> >    42d7395feb5 (mm: support more pagesizes for MAP_HUGETLB/SHM_HUGETLB)
> >
> > It unnecessarily adds another layer, specific to sysv shm, without
> > anything special about it: the macros are identical to the MAP_HUGE_*
> > stuff, which in turn does correctly describe the hugepage subsystem.
> >
> > One example of the problems with extra layers what this patch fixes:
> > mmap_pgoff() should never be using SHM_HUGE_* logic. It is obviously
> > harmless but it would still be grand to get rid of it -- although
> > now in the manpages I don't see that happening.
>
> Can we just drop SHM_HUGE_MASK altogether? It is not exported in uapi
> headers AFAICS.

Yeah that was my original idea, however I noticed that shmget.2 mentions
kernel internals as part of SHM_HUGE_{2MB,1GB}, ie: SHM_HUGE_SHIFT. So
dropping _MASK doesn't make sense if we are going to keep _SHIFT.

Thanks,
Davidlohr