On Wed, Mar 20, 2024 at 05:40:39PM +0000, Christophe Leroy wrote:

Le 20/03/2024 à 17:09, Peter Xu a écrit :

quoted

On Wed, Mar 20, 2024 at 06:16:43AM +0000, Christophe Leroy wrote:

quoted

At the first place that was to get a close fit between hardware
pagetable topology and linux pagetable topology. But obviously we
already stepped back for 512k pages, so let's go one more step aside and
do similar with 8M pages.

I'll give it a try and see how it goes.

So you're talking about 8M only for 8xx, am I right?

Yes I am.

quoted

There seem to be other PowerPC systems use hugepd.  Is it possible that we
convert all hugepd into cont_pte form?

Indeed.

Seems like we have hugepd for book3s/64 and for nohash.

For book3s I don't know, may Aneesh can answer.

For nohash I think it should be possible because TLB misses are handled 
by software. Even the e6500 which has a hardware tablewalk falls back on 
software walk when it is a hugepage IIUC.

It'll be great if I can get some answer here, and then I know the path for
hugepd in general.  I don't want to add any new code into core mm to
something destined to fade away soon.

One option for me is I can check a macro of hugepd existance, so all new
code will only work when hugepd is not supported on such arch.  However
that'll start to make some PowerPC systems special (which I still tried
hard to avoid, if that wasn't proved in the past..), meanwhile we'll also
need to keep some generic-mm paths (that I can already remove along with
the new code) only for these hugepd systems.  But it's still okay to me,
it'll be just a matter of when to drop those codes, sooner or later.

Thanks,

-- 
Peter Xu