Re: Getting FS access events

[Daniel Phillips]

On Tuesday 15 May 2001 08:57, Alexander Viro wrote:
> On Tue, 15 May 2001, Richard Gooch wrote:
> > > What happens if you create a buffer cache entry? Does that
> > > invalidate the page cache one? Or do you just allow invalidates
> > > one way, and not the other? And why=
> >
> > I just figured on one way invalidates, because that seems cheap and
> > easy and has some benefits. Invalidating the other way is costly,
> > so don't bother, even if there were some benefits.
>
> Cute.
> 	* create an instance in pagecache
> 	* start reading into buffer cache (doesn't invalidate, right?)
> 	* start writing using pagecache
> 	* lose the page
> 	* try to read it (via pagecache)
> Woops - just found a copy in buffer cache, let's pick data from it.
> Pity that said data is obsolete...

That's because you left out his invalidate:

 	* create an instance in pagecache
 	* start reading into buffer cache (doesn't invalidate, right?)
 	* start writing using pagecache (invalidate buffer copy)
 	* lose the page
 	* try to read it (via pagecache)

Everthing ok.  As an optimization, instead of 'lose the page', do 'move 
page blocks to buffer cache'.

--
Daniel