Re: RWF_DONTCACHE regression fix for xfs

[Tal Zussman <tz2294@columbia.edu>]

On 8/10/26 10:45 AM, Christoph Hellwig wrote:
> Below is Tal's suggested fixup for xfs with the whitespace damage fixeѕ.
> It should probably be attributed to Tal instead.  Can you handled it
> from here and send it to Jens with your signoff/authorship to avoid
> the performance regression in XFS?
> 

Yes, will do shortly. Thanks Christoph!

> From: Christoph Hellwig <hch@lst.de>
> Subject: xfs: avoid double deferrals for RWF_DONTCACHE writes
> 
> XFS already defers some writes to a workqueue when transactions are
> needed to process the I/O completion.  Disable the block layer bio
> task completion in this case to avoid a major performance drop.
> 
> Fixes: efbde6f9f449 ("iomap: use BIO_COMPLETE_IN_TASK for dropbehind writeback")
> ---
>   fs/xfs/xfs_aops.c | 15 +++++++++++++--
>   1 file changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
> index f73e26d9c9f9..059846a8d65c 100644
> --- a/fs/xfs/xfs_aops.c
> +++ b/fs/xfs/xfs_aops.c
> @@ -372,10 +372,14 @@ xfs_writeback_submit(
>   	}
>   
>   	/*
> -	 * Send ioends that might require a transaction to the completion wq.
> +	 * Send ioends that might require a transaction to the completion wq,
> +	 * and disable the block layer task completion for them as there is no
> +	 * need to defer twice.
>   	 */
> -	if (xfs_ioend_needs_wq_completion(ioend))
> +	if (xfs_ioend_needs_wq_completion(ioend)) {
>   		ioend->io_bio.bi_end_io = xfs_end_bio;
> +		bio_clear_flag(&ioend->io_bio, BIO_COMPLETE_IN_TASK);
> +	}
>   
>   	return iomap_ioend_writeback_submit(wpc, error);
>   }
> @@ -481,7 +485,14 @@ xfs_zoned_writeback_submit(
>   {
>   	struct iomap_ioend		*ioend = wpc->wb_ctx;
>   
> +	/*
> +	 * Defer all completions to our workqueue as all zoned writes require a
> +	 * transaction to be persisted.  This also means we never need the block
> +	 * layer in-task completion for a task context.
> +	 */
>   	ioend->io_bio.bi_end_io = xfs_end_bio;
> +	bio_clear_flag(&ioend->io_bio, BIO_COMPLETE_IN_TASK);
> +
>   	if (error) {
>   		ioend->io_bio.bi_status = errno_to_blk_status(error);
>   		bio_endio(&ioend->io_bio);
> -- 
> 2.53.0
>