linux-kernel - Re: [PATCH 1/2] netfs: Fix copy-to-cache so that it performs collection with ceph+fscache

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Message-ID: <CAKPOu+-Qsy0cr7XH1FsJbBxQpjmsK2swz-ptexaRvEM+oMGknA@mail.gmail.com>
Date: Sat, 12 Jul 2025 07:25:08 +0200
From: Max Kellermann <max.kellermann@...os.com>
To: David Howells <dhowells@...hat.com>
Cc: Christian Brauner <christian@...uner.io>, Paulo Alcantara <pc@...guebit.com>, 
	Viacheslav Dubeyko <slava@...eyko.com>, Alex Markuze <amarkuze@...hat.com>, 
	Ilya Dryomov <idryomov@...il.com>, netfs@...ts.linux.dev, linux-nfs@...r.kernel.org, 
	ceph-devel@...r.kernel.org, linux-fsdevel@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Paulo Alcantara <pc@...guebit.org>, stable@...r.kernel.org
Subject: Re: [PATCH 1/2] netfs: Fix copy-to-cache so that it performs
 collection with ceph+fscache

On Fri, Jul 11, 2025 at 5:10 PM David Howells <dhowells@...hat.com> wrote:
>
> The netfs copy-to-cache that is used by Ceph with local caching sets up a
> new request to write data just read to the cache.  The request is started
> and then left to look after itself whilst the app continues.  The request
> gets notified by the backing fs upon completion of the async DIO write, but
> then tries to wake up the app because NETFS_RREQ_OFFLOAD_COLLECTION isn't
> set - but the app isn't waiting there, and so the request just hangs.
>
> Fix this by setting NETFS_RREQ_OFFLOAD_COLLECTION which causes the
> notification from the backing filesystem to put the collection onto a work
> queue instead.

Thanks David, you can add me as Tested-by if you want.

I can't test the other patch for the next two weeks (vacation). When
I'm back, I'll install both fixes on some heavily loaded production
machines - our clusters always shake out the worst in every piece of
code they run!