Re: NR_UNSTABLE_FS vs. NR_FILE_DIRTY: double counting pages?

[Ethan Solomita <solo@google.com>]

Trond Myklebust wrote:
> On Fri, 2007-04-27 at 18:21 -0700, Ethan Solomita wrote:
> > 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
>
> It should not happen. If the page is on the unstable list, then it will
> be committed before nfs_updatepage is allowed to redirty it. See the
> recent fixes in 2.6.21-rc7.

	Above I present a codepath called straight from sys_write() which seems 
to do what I say. I could be wrong, but can you address the code paths I 
show above which seem to set both?
	-- Ethan
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