Re: [PATCH 1/3] mm: add vm_insert_mixed_mkwrite()

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(a)linux.intel.com&gt; --- 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);

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); +}