[PATCH 03/27] xfs: use write_cache_pages for writeback clustering

[Christoph Hellwig]

> 
> This piece of logic checks is the type of buffer has changed from the
> previous buffer. This used to work just fine, but now "type" is
> local to the __xfs_vm_writepage() function, while the imap life
> span?? multiple calls to the __xfs_vm_writepage() function. Hence
> type is reinitialised to IO_OVERWRITE on every page that written,
> and so for delalloc we are invalidating the imap and looking it up
> again on every page. Traces show this sort of behaviour:

Ah crap.  I actually had it that way initially, but it got lost during
a rebase due to a minimal context change screwing most hunks of the
patch.

Thanks for tracking this down!