On Wed, 2007-01-24 at 09:37 +1100, David Chinner wrote:
With the recent changes to cancel_dirty_pages(), XFS will
dump warnings in the syslog because it can truncate_inode_pages()
on dirty mapped pages.
I've determined that this is indeed correct behaviour for XFS
as this can happen in the case of races on mmap()d files with
direct I/O. In this case when we do a direct I/O read, we
flush the dirty pages to disk, then truncate them out of the
page cache. Unfortunately, between the flush and the truncate
the mmap could dirty the page again. At this point we toss a
dirty page that is mapped.
This sounds iffy, why not just leave the page in the pagecache if its
mapped anyway?
None of the existing functions for truncating pages or invalidating
pages work in this situation. Invalidating a page only works for
non-dirty pages with non-dirty buffers, and they only work for
whole pages and XFS requires partial page truncation.
On top of that the page invalidation functions don't actually
call into the filesystem to invalidate the page and so the filesystem
can't actually invalidate the page properly (e.g. do stuff based on
private buffer head flags).
Have you seen the new launder_page() a_op? called from
invalidate_inode_pages2_range()