Re: [PATCH 10/28] FS-Cache: Recruit a couple of page flags for cache management [try #2]

[David Howells]

Nick Piggin <nickpiggin@xxxxxxxxxxxx> wrote:

> > > I'd much prefer if you would handle this in the filesystem, and have it
> > > set PG_private whenever fscache needs to receive a callback, and DTRT
> > > depending on whether PG_fscache etc. is set or not.
> >
> > That's tricky and slower[*].  One of the things I want to do is to modify
> > iso9660 to do be able to do caching, but PG_private is 'owned' by the
> > generic buffer cache code.
> 
> Maybe it is harder, but it is the right way to do it.

You're wrong.  It would mean that PG_private is the logical disjunction of
PG_fscache and some condition not otherwise explicitly stored.  I tried that
with NFS and it was nasty.

As you can no doubt see, it means that you can't distinguish all the states
you used to be able to.

> So you should modify the filesystems rather than core code.

I think you missed what I said:

	but PG_private is 'owned' by the generic buffer cache code.

That means more of the core code would have to change - or, at least, change
more.

David
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