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.2.23.453.2011221300100.2830...@chino.kir.corp.google.com Anyway, I agree with your other arguments and this patchset. Thanks.
