Re: [PATCH] md: stop using do_sync_mapping_range

[Christoph Hellwig <hch@lst.de>]

On Wed, Sep 23, 2009 at 02:47:15PM +0100, Jamie Lokier wrote:
> Christoph Hellwig wrote:
> > -		do_sync_mapping_range(file->f_mapping, 0, LLONG_MAX,
> > -				      SYNC_FILE_RANGE_WAIT_BEFORE |
> > -				      SYNC_FILE_RANGE_WRITE |
> > -				      SYNC_FILE_RANGE_WAIT_AFTER);
> > +		filemap_write_and_wait(file->f_mapping);
> >
> > It's a very awkward way to write out all data and wait for it, so just
> > call filemap_write_and_wait.  I still can't figure what the point of
> > all this is, so a comment would surely be helpful.
> 
> The SYNC_FILE_RANGE_WAIT_BEFORE is to make sure that writes which were
> started before the most recent dirtying are completed before
> initiating a second write on the same pages to make sure the most
> recently dirty data is written.
> 
> Does filemap_write_and_wait() do that?

Yes, for WB_SYNC_ALL syncs write_cache_pages or the fs-specific
equivalent waits for pages marked writeback before starting starting
the writeout.