NR_UNSTABLE_FS vs. NR_FILE_DIRTY: double counting pages?

[Ethan Solomita <solo@google.com>]

    There are several places where we add together NR_UNSTABLE_FS and
NF_FILE_DIRTY:

sync_inodes_sb()
balance_dirty_pages()
wakeup_pdflush()
wb_kupdate()
prefetch_suitable()

    I can trace a standard codepath where it seems both of these are set
on the same page:

nfs_file_aops.commit_write ->
    nfs_commit_write
    nfs_updatepages
    nfs_writepage_setup
    nfs_wb_page
    nfs_wb_page_priority
    nfs_writepage_locked
    nfs_flush_mapping
    nfs_flush_list
    nfs_flush_multi
    nfs_write_partial_ops.rpc_call_done
    nfs_writeback_done_partial
    nfs_writepage_release
    nfs_reschedule_unstable_write
    nfs_mark_request_commit
    incr NR_UNSTABLE_NFS

nfs_file_aops.commit_write ->
    nfs_commit_write
    nfs_updatepage
    __set_page_dirty_nobuffers
    incr NF_FILE_DIRTY


    This is the standard code path that derives from sys_write(). Can
someone either show how this code sequence can't happen, or confirm for
me that there's a bug?
    -- Ethan