+Dan Williams
+Sudarshan Rajagopalan
On Thu, Jul 7, 2022 at 12:17 AM Will Deacon <will@xxxxxxxxxx> wrote:
>
> On Tue, Jul 05, 2022 at 09:07:59PM +0800, Huacai Chen wrote:
> > On Tue, Jul 5, 2022 at 5:29 PM Will Deacon <will@xxxxxxxxxx> wrote:
> > > On Mon, Jul 04, 2022 at 07:25:25PM +0800, Huacai Chen wrote:
> > > > diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
> > > > index 33e2a1ceee72..6f2e40bb695d 100644
> > > > --- a/mm/sparse-vmemmap.c
> > > > +++ b/mm/sparse-vmemmap.c
> > > > @@ -686,6 +686,60 @@ int __meminit vmemmap_populate_basepages(unsigned long start, unsigned long end,
> > > > return vmemmap_populate_range(start, end, node, altmap, NULL);
> > > > }
> > > >
> > > > +void __weak __meminit vmemmap_set_pmd(pmd_t *pmd, void *p, int node,
> > > > + unsigned long addr, unsigned long next)
> > > > +{
> > > > +}
> > > > +
> > > > +int __weak __meminit vmemmap_check_pmd(pmd_t *pmd, int node, unsigned long addr,
> > > > + unsigned long next)
> > > > +{
> > > > + return 0;
> > > > +}
> > > > +
> > > > +int __meminit vmemmap_populate_hugepages(unsigned long start, unsigned long end,
> > > > + int node, struct vmem_altmap *altmap)
> > > > +{
> > > > + unsigned long addr;
> > > > + unsigned long next;
> > > > + pgd_t *pgd;
> > > > + p4d_t *p4d;
> > > > + pud_t *pud;
> > > > + pmd_t *pmd;
> > > > +
> > > > + for (addr = start; addr < end; addr = next) {
> > > > + next = pmd_addr_end(addr, end);
> > > > +
> > > > + pgd = vmemmap_pgd_populate(addr, node);
> > > > + if (!pgd)
> > > > + return -ENOMEM;
> > > > +
> > > > + p4d = vmemmap_p4d_populate(pgd, addr, node);
> > > > + if (!p4d)
> > > > + return -ENOMEM;
> > > > +
> > > > + pud = vmemmap_pud_populate(p4d, addr, node);
> > > > + if (!pud)
> > > > + return -ENOMEM;
> > > > +
> > > > + pmd = pmd_offset(pud, addr);
> > > > + if (pmd_none(READ_ONCE(*pmd))) {
> > > > + void *p;
> > > > +
> > > > + p = vmemmap_alloc_block_buf(PMD_SIZE, node, altmap);
> > > > + if (p) {
> > > > + vmemmap_set_pmd(pmd, p, node, addr, next);
> > > > + continue;
> > > > + } else if (altmap)
> > > > + return -ENOMEM; /* no fallback */
> > >
> > > Why do you return -ENOMEM if 'altmap' here? That seems to be different to
> > > what we currently have on arm64 and it's not clear to me why we're happy
> > > with an altmap for the pmd case, but not for the pte case.
> > The generic version is the same as X86. It seems that ARM64 always
> > fallback whether there is an altmap, but X86 only fallback in the no
> > altmap case. I don't know the reason of X86, can Dan Williams give
> > some explaination?
>
> Right, I think we need to understand the new behaviour here before we adopt
> it on arm64.
Hi, Dan,
Could you please tell us the reason? Thanks.
And Sudarshan,
You are the author of adding a fallback mechanism to ARM64, do you
know why ARM64 is different from X86 (only fallback in no altmap
case)?
Huacai
>
> Will
