On Wed, Jun 7, 2017 at 1:48 PM, Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx> wrote: > To be able to use the common 4k zero page in DAX we need to have our PTE > fault path look more like our PMD fault path where a PTE entry can be > marked as dirty and writeable as it is first inserted, rather than waiting > for a follow-up dax_pfn_mkwrite() => finish_mkwrite_fault() call. > > Right now we can rely on having a dax_pfn_mkwrite() call because we can > distinguish between these two cases in do_wp_page(): > > case 1: 4k zero page => writable DAX storage > case 2: read-only DAX storage => writeable DAX storage > > This distinction is made by via vm_normal_page(). vm_normal_page() returns > false for the common 4k zero page, though, just as it does for DAX ptes. > Instead of special casing the DAX + 4k zero page case, we will simplify our > DAX PTE page fault sequence so that it matches our DAX PMD sequence, and > get rid of dax_pfn_mkwrite() completely. > > This means that insert_pfn() needs to follow the lead of insert_pfn_pmd() > and allow us to pass in a 'mkwrite' flag. If 'mkwrite' is set insert_pfn() > will do the work that was previously done by wp_page_reuse() as part of the > dax_pfn_mkwrite() call path. > > Signed-off-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx> > --- > include/linux/mm.h | 9 +++++++-- > mm/memory.c | 21 ++++++++++++++------- > 2 files changed, 21 insertions(+), 9 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index b892e95..11e323a 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -2294,10 +2294,15 @@ int vm_insert_pfn(struct vm_area_struct *vma, unsigned long addr, > unsigned long pfn); > int vm_insert_pfn_prot(struct vm_area_struct *vma, unsigned long addr, > unsigned long pfn, pgprot_t pgprot); > -int vm_insert_mixed(struct vm_area_struct *vma, unsigned long addr, > - pfn_t pfn); > +int vm_insert_mixed_mkwrite(struct vm_area_struct *vma, unsigned long addr, > + pfn_t pfn, bool mkwrite); Are there any other planned public users of vm_insert_mixed_mkwrite() that would pass false? I think not. > int vm_iomap_memory(struct vm_area_struct *vma, phys_addr_t start, unsigned long len); > > +static inline int vm_insert_mixed(struct vm_area_struct *vma, > + unsigned long addr, pfn_t pfn) > +{ > + return vm_insert_mixed_mkwrite(vma, addr, pfn, false); > +} ...in other words instead of making the distinction of vm_insert_mixed_mkwrite() and vm_insert_mixed() with extra flag argument just move the distinction into mm/memory.c directly. So, the prototype remains the same as vm_insert_mixed() int vm_insert_mixed_mkwrite(struct vm_area_struct *vma, unsigned long addr, pfn_t pfn); ...and only static insert_pfn(...) needs to change.