[PATCH 0/6] mm: tracking dirty pages -v9

[Peter Zijlstra <a.p.zijlstra@chello.nl>]

The latest version of the tracking dirty pages patch-set.
On request against -mm.

This version handles VM_PFNMAP vmas and the COW case of shared RO mappings.

follow_page() got a comment for being weird, but in the light of the 
set_page_dirty() call that can not yet be removed does something sane.

copy_one_pte() also does the right thing, although I wonder why it clears
the dirty bit for children?

f_op->open() - sets a backing_dev_info
f_op->mmap() - modifies both vma->vm_flags and vma->vm_page_prot

Since our condition depends on both the backing_dev_info and vma->vm_flags
it cannot set vma->vm_page_prot before f_op->mmap().

However this means that !VM_PFNMAP vmas that are shared writable but do not
provide a f_op->nopage() and whos backing_dev_info does not have 
BDI_CAP_NO_ACCT_DIRTY, are left writable.

Peter