David Woodhouse wrote:
On Fri, 2021-02-12 at 14:19 -0600, Justin Forbes wrote:
> Just as there are many things that expect the 64K page size. I am not
> doing this.
I don't really find either of those to be compelling arguments, FWIW.
If we have broken code which makes assumptions about page sizes, we
should fix it. Whatever assumption it makes.
We certainly *shouldn't* have assumptions like that in userspace, and
we *shouldn't* need to rebuild userspace for such a change.
For a long time we had 4KiB pages on ppc32 AND 64KiB pages on ppc64,
and we fixed things to use getpagesize() instead of hard-coding any
value at all. It's possible that we have regressions, but we should
probably fix those.
I think that all architectures should use the same page size if it is
technically possible. I do not see any valid reason for ppc64le to be
special there.
Once upon a time when we still supported the PS3, the 64KiB page
size
was fairly painful and inefficient there but IBM forced it because it
apparently gave a significant performance win on boxes and workloads
that they actually cared about. These days, I think the arguments for
64KiB are certainly no *less* compelling than they were then, when I
conceded the change.
The input of the CPU manufacturer is certainly valid, but it should not be
the only criterion for such a decision. Portability concerns should also be
considered.
The fact that 64 KiB is not even the right choice for all ppc64le machines
only makes it even more questionable to make a different tradeoff there than
on other platforms, even if the main counterexample is now obsolete.
Kevin Kofler