On Tue, Apr 19, 2022 at 11:13:48AM -0400, Johannes Weiner wrote: > Hi Peter, Hi, Johannes, > > On Mon, Apr 04, 2022 at 09:49:29PM -0400, Peter Xu wrote: > > Enable PTE markers by default. On x86_64 it means it'll auto-enable > > PTE_MARKER_UFFD_WP as well. > > > > Signed-off-by: Peter Xu <peterx@xxxxxxxxxx> > > --- > > mm/Kconfig | 2 ++ > > 1 file changed, 2 insertions(+) > > > > diff --git a/mm/Kconfig b/mm/Kconfig > > index 6e7c2d59fa96..3eca34c864c5 100644 > > --- a/mm/Kconfig > > +++ b/mm/Kconfig > > @@ -911,12 +911,14 @@ config ANON_VMA_NAME > > > > config PTE_MARKER > > bool "Marker PTEs support" > > + default y > > > > help > > Allows to create marker PTEs for file-backed memory. > > make oldconfig just prompted me on these: > > --- > Marker PTEs support (PTE_MARKER) [Y/n/?] (NEW) ? > > CONFIG_PTE_MARKER: > > Allows to create marker PTEs for file-backed memory. > > Symbol: PTE_MARKER [=y] > Type : bool > Defined at mm/Kconfig:1046 > Prompt: Marker PTEs support > Location: > Main menu > -> Memory Management options > --- > > > config PTE_MARKER_UFFD_WP > > bool "Marker PTEs support for userfaultfd write protection" > > + default y > > depends on PTE_MARKER && HAVE_ARCH_USERFAULTFD_WP > > It's not possible to answer them without looking at the code. > > But after looking at the code, I'm still not sure why it asks > me. Isn't this infrastructure code? > > Wouldn't it make more sense to remove the prompt string and have > userfaultfd simply select those? > > If this is too experimental to enable per default, a more reasonable > question for the user would be a "userfaultfd file support" option or > something, and have *that* select the marker code. Thanks for raising this question. Actually it's right now enabled by default, so I kept the options just to make sure we can always explicitly disable those options when we want. That's majorly why I kept this patch standalone one so if we want we can even drop it. Said that, I fully agree with you that having two options seem to be an overkill, especially the PTE_MARKER option will be too challenging to be correctly understood by anyone not familiar with it. So after a 2nd thought I'm trying to refine what I want to achieve with the kbuild system on this new feature: - On supported systems (x86_64), should be by default y with "make olddefconfig", but able to turn it off using "make oldconfig" etc., so the user will have a choice when they want. - On not-supported systems (non-x86_64), should be always n without any prompt asking, and user won't even see this entry. - PTE_MARKER option should always be hidden for all archs I plan to post a patch that is attached (I also reworded the entry to not mention about pte markers). Does that look acceptable on your side? Thanks, -- Peter Xu
