Re: [PATCH 0/6] prohibit pinning pages in ZONE_MOVABLE

[Joonsoo Kim]

On Fri, Dec 04, 2020 at 12:50:56PM -0500, Pavel Tatashin wrote:
> > > Yes, this indeed could be a problem for some configurations. I will
> > > add your comment to the commit log of one of the patches.
> >
> > It sounds like there is some inherent tension here, breaking THP's
> > when doing pin_user_pages() is a really nasty thing to do. DMA
> > benefits greatly from THP.
> >
> > I know nothing about ZONE_MOVABLE, is this auto-setup or an admin
> > option? If the result of this patch is standard systems can no longer
> > pin > 80% of their memory I have some regression concerns..
> 
> ZONE_MOVABLE can be configured via kernel parameter, or when memory
> nodes are onlined after hot-add; so this is something that admins
> configure. ZONE_MOVABLE is designed to gurantee memory hot-plug

Just note, the origin of ZONE_MOVABLE is to provide availability of
huge page, especially, hugetlb page. AFAIK, not guarantee memory
hot-plug. See following commit that introduces the ZONE_MOVABLE.

2a1e274 Create the ZONE_MOVABLE zone

> functionality, and not availability of THP, however, I did not know
> about the use case where some admins might configure ZONE_MOVABLE to

The usecase is lightly mentioned in previous discussion.

http://lkml.kernel.org/r/alpine.DEB.2.23.453.2011221300100.2830030@xxxxxxxxxxxxxxxxxxxxxxxxx

Anyway, I agree with your other arguments and this patchset.

Thanks.