On Wed, Dec 16, 2020 at 02:08:30PM -0800, Mike Kravetz wrote:
> > + * vmemmap_rmap_walk - walk vmemmap page table
>
> I am not sure if 'rmap' should be part of these names. rmap today is mostly
> about reverse mapping lookup. Did you use rmap for 'remap', or because this
> code is patterned after the page table walking rmap code? Just think the
> naming could cause some confusion.
I also had the same feeling about the 'rmap' usage.
> > +
> > +static void vmemmap_pte_range(pmd_t *pmd, unsigned long addr,
> > + unsigned long end, struct vmemmap_rmap_walk *walk)
> > +{
> > + pte_t *pte;
> > +
> > + pte = pte_offset_kernel(pmd, addr);
> > + do {
> > + BUG_ON(pte_none(*pte));
> > +
> > + if (!walk->reuse)
> > + walk->reuse = pte_page(pte[VMEMMAP_TAIL_PAGE_REUSE]);
>
> It may be just me, but I don't like the pte[-1] here. It certainly does work
> as designed because we want to remap all pages in the range to the page before
> the range (at offset -1). But, we do not really validate this 'reuse' page.
> There is the BUG_ON(pte_none(*pte)) as a sanity check, but we do nothing similar
> for pte[-1]. Based on the usage for HugeTLB pages, we can be confident that
> pte[-1] is actually a pte. In discussions with Oscar, you mentioned another
> possible use for these routines.
Without giving it much of a thought, I guess we could duplicate the
BUG_ON for the pte outside the loop, and add a new one for pte[-1].
Also, since walk->reuse seems to not change once it is set, we can take
it outside the loop? e.g:
pte *pte;
pte = pte_offset_kernel(pmd, addr);
BUG_ON(pte_none(*pte));
BUG_ON(pte_none(pte[VMEMMAP_TAIL_PAGE_REUSE]));
walk->reuse = pte_page(pte[VMEMMAP_TAIL_PAGE_REUSE]);
do {
....
} while...
Or I am not sure whether we want to keep it inside the loop in case
future cases change walk->reuse during the operation.
But to be honest, I do not think it is realistic of all future possible
uses of this, so I would rather keep it simple for now.
--
Oscar Salvador
SUSE L3
