Re: [PATCH] powerpc/mm: Implemented default_hugepagesz verification for powerpc

[victora]

Em 2017-07-05 01:26, Aneesh Kumar K.V escreveu:
> On Tuesday 04 July 2017 01:35 AM, Victor Aoqui wrote:
> > Implemented default hugepage size verification (default_hugepagesz=)
> > in order to allow allocation of defined number of pages (hugepages=)
> > only for supported hugepage sizes.
> >
> > Signed-off-by: Victor Aoqui <victora@xxxxxxxxxx>
> > ---
> >   arch/powerpc/mm/hugetlbpage.c | 15 +++++++++++++++
> >   1 file changed, 15 insertions(+)
> >
> > diff --git a/arch/powerpc/mm/hugetlbpage.c 
> > b/arch/powerpc/mm/hugetlbpage.c
> > index a4f33de..464e72e 100644
> > --- a/arch/powerpc/mm/hugetlbpage.c
> > +++ b/arch/powerpc/mm/hugetlbpage.c
> > @@ -797,6 +797,21 @@ static int __init hugepage_setup_sz(char *str)
> >   }
> >   __setup("hugepagesz=", hugepage_setup_sz);
> >
> > +static int __init default_hugepage_setup_sz(char *str)
> > +{
> > +        unsigned long long size;
> > +
> > +        size = memparse(str, &str);
> > +
> > +        if (add_huge_page_size(size) != 0) {
> > +                hugetlb_bad_size();
> > +                pr_err("Invalid default huge page size 
> > specified(%llu)\n", size);
> > +        }
> > +
> > +        return 1;
> > +}
> > +__setup("default_hugepagesz=", default_hugepage_setup_sz);
>
> isn't that a behavior change in what we have now ? . Right now if size
> specified is not supported, we fallback to HPAGE_SIZE.

Yes, it is. However, is this a correct behavior? If we specify an 
unsupported value, for example default_hugepagesz=1M and hugepages=1000, 
1M will be ignored and 1000 pages of 16M (arch default) will be 
allocated. This could lead to non-expected out of of memory/performance 
issue.

> mm/hugetlb.c
>
> if (!size_to_hstate(default_hstate_size)) {
> 	default_hstate_size = HPAGE_SIZE;
> 	if (!size_to_hstate(default_hstate_size))
> 		hugetlb_add_hstate(HUGETLB_PAGE_ORDER);
> }
>
>
> > +
> >   struct kmem_cache *hugepte_cache;
> >   static int __init hugetlbpage_init(void)
> >   {
>
> Even if we want to do this, this should be done in generic code and
> should not be powerpc specific

The verification of supported powerpc hugepage size (hugepagesz=) is 
being performed on add_huge_page_size(), which is currently defined in 
arch/powerpc/mm/hugetlbpage.c. I think it makes more sense to implement 
default_hugepagesz= verification on arch/powerpc, don't you think?

> -aneesh