Re: TAKE 964002 - Don't wait for pending I/Os when purging blocks beyond eof.

[Christoph Hellwig <hch@xxxxxxxxxxxxx>]

On Mon, Dec 10, 2007 at 04:59:55PM +1100, Lachlan McIlroy wrote:
> Don't wait for pending I/Os when purging blocks beyond eof.
> 
> On last close of a file we purge blocks beyond eof.  The same
> code is used when we truncate the file size down.  In this case
> we need to wait for any pending I/Os for dirty pages beyond the
> new eof.  For the last close case we are not changing the file
> size and therefore do not need to wait for any I/Os to complete.
> This fixes a performance bottleneck where writes into the page
> cache and cache flushes can become mutually exclusive.

I think I shortened from of this should be in the comment above
the conditional vn_iowait intead of the current

        /* wait for the completion of any pending DIOs */

which is wrong given that we don't wait for all pending direct I/O
requests..  (and vn_iowait doesn't wait for direct I/O anyway)