Re: [PATCH 4/4] mm/gup: remove get_user_pages_locked()

[John Hubbard <jhubbard@xxxxxxxxxx>]

On 1/31/22 05:36, Jason Gunthorpe wrote:
...
> > @@ -968,15 +966,15 @@ static long do_get_mempolicy(int *policy, nodemask_t *nmask,
> >   	if (flags & MPOL_F_NODE) {
> >   		if (flags & MPOL_F_ADDR) {
> >   			/*
> > -			 * Take a refcount on the mpol, lookup_node()
> > -			 * will drop the mmap_lock, so after calling
> > -			 * lookup_node() only "pol" remains valid, "vma"
> > -			 * is stale.
> > +			 * Take a refcount on the mpol, because we are about to
> > +			 * drop the mmap_lock, after which only "pol" remains
> > +			 * valid, "vma" is stale.
> >   			 */
> >   			pol_refcount = pol;
> >   			vma = NULL;
> >   			mpol_get(pol);
> >   			err = lookup_node(mm, addr);
> > +			mmap_read_unlock(mm);
>
> How about move the mmap_read_unlock up one line and then use
> get_user_pages_fast()
>
> I'm guessing in most cases here the PTE will be present so that should
> be a net win?

Neat, I'll do that.


thanks,
--
John Hubbard
NVIDIA