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
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