Re: [PATCH 1/5] prctl: extend PR_SET_THP_DISABLE to optionally exclude VM_HUGEPAGE

[David Hildenbrand]

Thanks Lorenzo for the review, I'll leave handling all that to Usama 
from this point :)

On 31.07.25 10:29, Lorenzo Stoakes wrote:
> Just a ping on the man page stuff - you will do that right? :>)

I'm hoping that Usama can take over that part. If not, I'll handle it 
(had planned it for once it's in mm-stable / going upstream).

[ ... ]

> > > > +/*
> > > > + * Don't disable THPs when explicitly advised (e.g., MADV_HUGEPAGE /
> > > > + * VM_HUGEPAGE).
> > > > + */
> > > > +# define PR_THP_DISABLE_EXCEPT_ADVISED	(1 << 1)
> > >
> > > NO space after # please.
> >
> > I think this is following the file convention, the space is there in other flags
> > all over this file. I dont like the space as well.
>
> Yeah yuck. It's not a big deal, but ideally I'd prefer us to be sane even
> if the rest of the header is less so here.

I'm afraid us doing something different here will not make prctl() any 
better as a whole, so let's keep it consistent in this questionable file.

> > > >   #define PR_GET_THP_DISABLE	42
> > > >
> > > >   /*
> > > > diff --git a/kernel/sys.c b/kernel/sys.c
> > > > index b153fb345ada..b87d0acaab0b 100644
> > > > --- a/kernel/sys.c
> > > > +++ b/kernel/sys.c
> > > > @@ -2423,6 +2423,50 @@ static int prctl_get_auxv(void __user *addr, unsigned long len)
> > > >   	return sizeof(mm->saved_auxv);
> > > >   }
> > > >
> > > > +static int prctl_get_thp_disable(unsigned long arg2, unsigned long arg3,
> > > > +				 unsigned long arg4, unsigned long arg5)
> > > > +{
> > > > +	unsigned long *mm_flags = &current->mm->flags;
> > > > +
> > > > +	if (arg2 || arg3 || arg4 || arg5)
> > > > +		return -EINVAL;
> > > > +
> > >
> > > Can we have a comment here about what we're doing below re: the return
> > > value?
> >
> > Do you mean add returning 1 for MMF_DISABLE_THP_COMPLETELY and 3 for MMF_DISABLE_THP_EXCEPT_ADVISED?
>
> Well more so something about we return essentially flags indicating what is
> enabled or not, if bit 0 is set then it's disabled, if bit 1 is set then
> it's that with the exception of VM_HUGEPAGE VMAs.

We have that documented above the defines for flags etc. Maybe simply here:

/* If disabled, we return "1 | flags", otherwise 0. */

--
Cheers,

David / dhildenb