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

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Date:   Thu, 21 Oct 2021 15:20:36 -0700
From:   Omar Sandoval <osandov@...ndov.com>
To:     David Howells <dhowells@...hat.com>
Cc:     linux-cachefs@...hat.com, ceph-devel@...r.kernel.org,
        linux-afs@...ts.infradead.org,
        Anna Schumaker <anna.schumaker@...app.com>,
        linux-nfs@...r.kernel.org,
        Kent Overstreet <kent.overstreet@...il.com>,
        linux-mm@...ck.org, Matthew Wilcox <willy@...radead.org>,
        linux-fsdevel@...r.kernel.org,
        Dave Wysochanski <dwysocha@...hat.com>,
        Marc Dionne <marc.dionne@...istor.com>,
        Trond Myklebust <trond.myklebust@...merspace.com>,
        Shyam Prasad N <nspmangalore@...il.com>,
        Eric Van Hensbergen <ericvh@...il.com>,
        v9fs-developer@...ts.sourceforge.net, linux-cifs@...r.kernel.org,
        Latchesar Ionkov <lucho@...kov.net>,
        Jeff Layton <jlayton@...nel.org>,
        Steve French <sfrench@...ba.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Dominique Martinet <asmadeus@...ewreck.org>,
        Ilya Dryomov <idryomov@...il.com>,
        Trond Myklebust <trondmy@...merspace.com>,
        Jeff Layton <jlayton@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 00/67] fscache: Rewrite index API and management system

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/