Re: [RFC][patch 0/2] mm: remove PageReserved

[Daniel Phillips <phillips@arcor.de>]

On Monday 15 August 2005 23:15, David Howells wrote:
> I want to know when a page is going to be modified so that I
> can predict the state of the cache as much as possible. I don't want
> userspace processes corrupting the cache in unrecorded ways.

There are two cases:

  1) Metadata.  If anybody is doing racy writes to metadata pages, it is
     your filesystem, and you have a bug.

  2) Data.  In Linux practice and Posix, racy writes to files have
     undefined semantics, including the possibility that data may end up
     interleaved on a disk block.

You seem to be trying to define (2) as "corruption" and setting out to prevent 
it.  But it is not the responsibility of a filesystem to prevent this, it is 
the responsibility of the application.

Could you please explain why it is not ok to end up with a half-written page 
in your cache, if the client was in fact halfway through writing it when it 
crashed?

Regards,

Daniel