On Wed, Feb 21, 2024 at 05:37:37PM +0800, Peter Xu wrote: > On Mon, Jan 15, 2024 at 01:55:51PM -0400, Jason Gunthorpe wrote: > > On Wed, Jan 03, 2024 at 05:14:13PM +0800, peterx@xxxxxxxxxx wrote: > > > From: Peter Xu <peterx@xxxxxxxxxx> > > > > > > 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@xxxxxxxxxx> > > > --- > > > 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.. > > I think I mostly agree with you, and these APIs are indeed confusing. IMHO > the challenge is about the risk of breaking others on small changes in the > details where evil resides. These APIs are super confusing, which is why I brought it up.. Adding even more subtly different variations is not helping. I think pmd_leaf means the entry is present and refers to a physical page not another radix level. > > 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; > > For example, here I don't think it's strictly pmd_leaf()? As pmd_huge() > will return true if PRESENT=0 && PSE=0 (as long as none pte ruled out > first), while pmd_leaf() will return false; I think that came from > cbef8478bee5. Yikes, but do you even want to handle non-present entries in GUP world? Isn't everything gated by !present in the first place? > Besides that, there're also other cases where it's not clear of such direct > replacement, not until further investigated. E.g., arm-3level has: > > #define pmd_leaf(pmd) pmd_sect(pmd) > #define pmd_sect(pmd) ((pmd_val(pmd) & PMD_TYPE_MASK) == \ > PMD_TYPE_SECT) > #define PMD_TYPE_SECT (_AT(pmdval_t, 1) << 0) > > While pmd_huge() there relies on PMD_TABLE_BIT () I looked at tht, it looked OK.. #define PMD_TYPE_MASK (_AT(pmdval_t, 3) << 0) #define PMD_TABLE_BIT (_AT(pmdval_t, 1) << 1) It is the same stuff, just a little confusingly written Jason
