Re: [PATCH 02/14] FS-Cache: Recruit a couple of page flags for cache management

[David Howells <dhowells@redhat.com>]

Peter Zijlstra <peterz@infradead.org> wrote:

> Not sure its a good idea to overload page_has_private() with an
> overloadable page-flag. What if some future FS wants to use
> PG_owner_priv_2 for other purposes?

All that it means is that releasepage() and co will get called if a page is to
be released or invalidated that has that bit set.  I think that's something a
future FS could probably live with.

However, I do have to trigger a call to releasepage() and co *somehow*.

> Obviously filesystems cannot use these two page-flags if they want to be
> compatible with FS-cache, but need all filesystems be?

What do you mean?  That's why I went for the PG_owner_priv_* approach rather
than just naming the bits unto FS-Cache directly.

> (also, ouch! - 2 pageflags)

Yeah.  The consequence of having things asynchronous is that you have to find
signalling mechanisms to synchronise around the asynchronicity:-/

Furthermore, it occurs to me that I can't use PG_private or page->private to
store this information because I want to make isofs use caching, and those two
pieces of information are owned by the buffering code.

David