On Tue, 3 Dec 2019 14:22:32 +0100 Thomas Hellström (VMware) thomas_os@shipmail.org wrote:
From: Thomas Hellstrom thellstrom@vmware.com
For VM_PFNMAP and VM_MIXEDMAP vmas that want to support transhuge pages and -page table entries, introduce vma_is_special_huge() that takes the same codepaths as vma_is_dax().
The use of "special" follows the definition in memory.c, vm_normal_page(): "Special" mappings do not wish to be associated with a "struct page" (either it doesn't exist, or it exists but they don't want to touch it)
For PAGE_SIZE pages, "special" is determined per page table entry to be able to deal with COW pages. But since we don't have huge COW pages, we can classify a vma as either "special huge" or "normal huge".
--- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -2822,6 +2822,12 @@ extern long copy_huge_page_from_user(struct page *dst_page, const void __user *usr_src, unsigned int pages_per_huge_page, bool allow_pagefault); +static inline bool vma_is_special_huge(struct vm_area_struct *vma) +{
- return vma_is_dax(vma) || (vma->vm_file &&
(vma->vm_flags & (VM_PFNMAP | VM_MIXEDMAP)));+}
Some documetnation would be nice. Not only what it does, but why it does it. ie, what is the *meaning* of vma_is_spacial_huge(vma)==true?