Messages in this thread Patch in this message | | | Date | Mon, 15 Jan 2024 13:55:51 -0400 | From | Jason Gunthorpe <> | Subject | Re: [PATCH v2 03/13] mm: Provide generic pmd_thp_or_huge() |
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On Wed, Jan 03, 2024 at 05:14:13PM +0800, peterx@redhat.com wrote: > From: Peter Xu <peterx@redhat.com> > > ARM defines pmd_thp_or_huge(), detecting either a THP or a huge PMD. It > can be a helpful helper if we want to merge more THP and hugetlb code > paths. Make it a generic default implementation, only exist when > CONFIG_MMU. Arch can overwrite it by defining its own version. > > For example, ARM's pgtable-2level.h defines it to always return false. > > Keep the macro declared with all config, it should be optimized to a false > anyway if !THP && !HUGETLB. > > Signed-off-by: Peter Xu <peterx@redhat.com> > --- > include/linux/pgtable.h | 4 ++++ > mm/gup.c | 3 +-- > 2 files changed, 5 insertions(+), 2 deletions(-) > > diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h > index 466cf477551a..2b42e95a4e3a 100644 > --- a/include/linux/pgtable.h > +++ b/include/linux/pgtable.h > @@ -1362,6 +1362,10 @@ static inline int pmd_write(pmd_t pmd) > #endif /* pmd_write */ > #endif /* CONFIG_TRANSPARENT_HUGEPAGE */ > > +#ifndef pmd_thp_or_huge > +#define pmd_thp_or_huge(pmd) (pmd_huge(pmd) || pmd_trans_huge(pmd)) > +#endif
Why not just use pmd_leaf() ?
This GUP case seems to me exactly like what pmd_leaf() should really do and be used for..
eg x86 does:
#define pmd_leaf pmd_large static inline int pmd_large(pmd_t pte) return pmd_flags(pte) & _PAGE_PSE;
static inline int pmd_trans_huge(pmd_t pmd) return (pmd_val(pmd) & (_PAGE_PSE|_PAGE_DEVMAP)) == _PAGE_PSE;
int pmd_huge(pmd_t pmd) return !pmd_none(pmd) && (pmd_val(pmd) & (_PAGE_PRESENT|_PAGE_PSE)) != _PAGE_PRESENT;
I spot checked a couple arches and it looks like it holds up.
Further, it looks to me like this site in GUP is the only core code caller..
So, I'd suggest a small series to go arch by arch and convert the arch to use pmd_huge() == pmd_leaf(). Then retire pmd_huge() as a public API.
> diff --git a/mm/gup.c b/mm/gup.c > index df83182ec72d..eebae70d2465 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -3004,8 +3004,7 @@ static int gup_pmd_range(pud_t *pudp, pud_t pud, unsigned long addr, unsigned lo > if (!pmd_present(pmd)) > return 0; > > - if (unlikely(pmd_trans_huge(pmd) || pmd_huge(pmd) || > - pmd_devmap(pmd))) { > + if (unlikely(pmd_thp_or_huge(pmd) || pmd_devmap(pmd))) { > /* See gup_pte_range() */ > if (pmd_protnone(pmd)) > return 0;
And the devmap thing here doesn't make any sense either. The arch should ensure that pmd_devmap() implies pmd_leaf(). Since devmap is a purely SW construct it almost certainly does already anyhow.
Jason
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