On Thu, Mar 28, 2019 at 01:33:42PM -0700, John Hubbard wrote: > On 3/25/19 7:40 AM, jglisse@xxxxxxxxxx wrote: > > From: Jérôme Glisse <jglisse@xxxxxxxxxx> > > > > To avoid random config build issue, select mmu notifier when HMM is > > selected. In any cases when HMM get selected it will be by users that > > will also wants the mmu notifier. > > > > Signed-off-by: Jérôme Glisse <jglisse@xxxxxxxxxx> > > Acked-by: Balbir Singh <bsingharora@xxxxxxxxx> > > Cc: Ralph Campbell <rcampbell@xxxxxxxxxx> > > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > > Cc: John Hubbard <jhubbard@xxxxxxxxxx> > > Cc: Dan Williams <dan.j.williams@xxxxxxxxx> > > --- > > mm/Kconfig | 1 + > > 1 file changed, 1 insertion(+) > > > > diff --git a/mm/Kconfig b/mm/Kconfig > > index 25c71eb8a7db..0d2944278d80 100644 > > --- a/mm/Kconfig > > +++ b/mm/Kconfig > > @@ -694,6 +694,7 @@ config DEV_PAGEMAP_OPS > > > > config HMM > > bool > > + select MMU_NOTIFIER > > select MIGRATE_VMA_HELPER > > > > config HMM_MIRROR > > > > Yes, this is a good move, given that MMU notifiers are completely, > indispensably part of the HMM design and implementation. > > The alternative would also work, but it's not quite as good. I'm > listing it in order to forestall any debate: > > config HMM > bool > + depends on MMU_NOTIFIER > select MIGRATE_VMA_HELPER > > ...and "depends on" versus "select" is always a subtle question. But in > this case, I'd say that if someone wants HMM, there's no advantage in > making them know that they must first ensure MMU_NOTIFIER is enabled. > After poking around a bit I don't see any obvious downsides either. You can not depend on MMU_NOTIFIER it is one of the kernel config option that is not selectable. So any config that need MMU_NOTIFIER must select it. > > However, given that you're making this change, in order to avoid odd > redundancy, you should also do this: > > diff --git a/mm/Kconfig b/mm/Kconfig > index 0d2944278d80..2e6d24d783f7 100644 > --- a/mm/Kconfig > +++ b/mm/Kconfig > @@ -700,7 +700,6 @@ config HMM > config HMM_MIRROR > bool "HMM mirror CPU page table into a device page table" > depends on ARCH_HAS_HMM > - select MMU_NOTIFIER > select HMM > help > Select HMM_MIRROR if you want to mirror range of the CPU page table of a Because it is a select option no harm can come from that hence i do not remove but i can remove it. Cheers, Jérôme
