Re: [PATCH 2/6] Rename __lock_page to lock_page_slow

[Suparna Bhattacharya <suparna@in.ibm.com>]

On Sun, Jul 24, 2005 at 11:36:34PM +0100, Christoph Hellwig wrote:
> On Sun, Jul 24, 2005 at 11:17:02PM +0100, Christoph Hellwig wrote:
> > On Mon, Jun 20, 2005 at 09:54:04PM +0530, Suparna Bhattacharya wrote:
> > > In order to allow for interruptible and asynchronous versions of
> > > lock_page in conjunction with the wait_on_bit changes, we need to
> > > define low-level lock page routines which take an additional
> > > argument, i.e a wait queue entry and may return non-zero status,
> > > e.g -EINTR, -EIOCBRETRY, -EWOULDBLOCK etc. This patch renames 
> > > __lock_page to lock_page_slow, so that __lock_page and 
> > > __lock_page_slow can denote the versions which take a wait queue 
> > > parameter.
> > 
> > How many users that don't use a waitqueue parameter will be left
> > once all AIO patches go in?

Since these patches are intended only for aio reads and (O_SYNC) writes,
that still leaves most other users of regular lock_page() as they are.

> 
> Actually looking at the later patches we always seem to pass
> current->io_wait anyway, so is there a real point for having the
> argument?
> 

Having the parameter enables issual of synchronous lock_page() within
an AIO path, overriding current->io_wait, (for example, consider the case
of a page fault during AIO !), and thus avoids the need to convert and audit
more paths to handle -EIOCBRETRY propagation (though it is possible to
do so as and when the need arises). This is why I decided to keep this
parameter explicit at the low level, and let the caller decide how to
invoke it and handle the return value propagation.

Does that make sense ?

BTW, there is also a potential secondary benefit of a low level
primitive for asynchronous page IO operations etc directly usable
by kernel threads, without having to use the whole gamut of AIO
interfaces.

Thanks for reviewing the code !

Regards
Suparna

-- 
Suparna Bhattacharya (suparna@in.ibm.com)
Linux Technology Center
IBM Software Lab, India