Re: enable iomap dio write completions from interrupt context

[Damien Le Moal <dlemoal@kernel.org>]

On 11/12/25 16:21, Christoph Hellwig wrote:
> Hi all,
> 
> Currently iomap defers all write completions to interrupt context.  This
> was based on my assumption that no one cares about the latency of those
> to simplify the code vs the old direct-io.c.  It turns out someone cared,
> as Avi reported a lot of context switches with ScyllaDB, which at least
> in older kernels with workqueue scheduling issues caused really high
> tail latencies.
> 
> Fortunately allowing the direct completions is pretty easy with all the
> other iomap changes we had since.
> 
> While doing this I've also found dead code which gets removed (patch 1)
> and an incorrect assumption in zonefs that read completions are called
> in user context, which it assumes for it's error handling.  Fix this by
> always calling error completions from user context (patch 2).
> 
> Against the vfs/vfs-6.19.iomap branch.
> 
> Diffstat:
>  Documentation/filesystems/iomap/operations.rst |    4 
>  fs/backing-file.c                              |    6 -
>  fs/iomap/direct-io.c                           |  149 +++++++++++--------------
>  include/linux/fs.h                             |   43 +------
>  io_uring/rw.c                                  |   16 --
>  5 files changed, 81 insertions(+), 137 deletions(-)

Where is the zonefs change ? Missing a patch ?


-- 
Damien Le Moal
Western Digital Research