Re: [PATCH 00/67] fscache: Rewrite index API and management system

[Omar Sandoval <osandov@osandov.com>]

On Mon, Oct 18, 2021 at 03:50:15PM +0100, David Howells wrote:
> 
> Here's a set of patches that rewrites and simplifies the fscache index API
> to remove the complex operation scheduling and object state machine in
> favour of something much smaller and simpler.  It is built on top of the
> set of patches that removes the old API[1].
> 
> The operation scheduling API was intended to handle sequencing of cache
> operations, which were all required (where possible) to run asynchronously
> in parallel with the operations being done by the network filesystem, while
> allowing the cache to be brought online and offline and interrupt service
> with invalidation.
> 
> However, with the advent of the tmpfile capacity in the VFS, an opportunity
> arises to do invalidation much more easily, without having to wait for I/O
> that's actually in progress: Cachefiles can simply cut over its file
> pointer for the backing object attached to a cookie and abandon the
> in-progress I/O, dismissing it upon completion.
> 
> Future work there would involve using Omar Sandoval's vfs_link() with
> AT_LINK_REPLACE[2] to allow an extant file to be displaced by a new hard
> link from a tmpfile as currently I have to unlink the old file first.

I had forgotten about that. It'd be great to finish that someday, but
given the dead-end of the last discussion [1], we might need to hash it
out the next time we can convene in person.

1:https://lore.kernel.org/linux-fsdevel/364531.1579265357@warthog.procyon.org.uk/