Re: PATCH [2.4.0test10]: Kiobuf#02, fault-in fix

["Stephen C. Tweedie" <sct@redhat.com>]

Hi,

On Mon, Nov 06, 2000 at 11:34:57PM +0100, Andrea Arcangeli wrote:
> On Mon, Nov 06, 2000 at 04:54:16PM +0000, Stephen C. Tweedie wrote:
> 
> About the implementation of the missing VM infrastructure for handling page
> dirty at the physical pagecache layer, I'd suggest to change ramfs to use a new
> PG_protected bitfield with the current semantics of PG_dirty, and to use
> PG_dirty for the stuff that we must flush to disk.

PG_dirty works for some cases.  In particular, it works for any
filesystems which can safely ignore the struct file * in the writepage
address_space operation.  However, for things like NFS, we cannot ever
to arbitrary writeback to a file from the page cache --- we need the
user context of the original write in order to establish the
credentials for the server operation.

That's why my current bug-fix patch just does the writepage at the end
of the raw IO: it's a general fix which works for all mmap types.
Once that is in place, we can think about extending it so that
filesystems can provide a separate method for "flush" which honurs
PG_dirty.  For filesystems with such a flush method, marking a kiobuf
dirty would simply involve setting PG_dirty, but for others (such as
NFS) the mark_kiobuf_dirty would still have to do the full early
writepage.

Cheers,
 Stephen
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