Re: [PATCH 5.10] xfs: drop submit side trans alloc for append ioends

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Wed, Apr 19, 2023 at 07:18:13PM +0300, Amir Goldstein wrote:
> From: Brian Foster <bfoster@redhat.com>
> 
> commit 7cd3099f4925d7c15887d1940ebd65acd66100f5 upstream.
> 
> Per-inode ioend completion batching has a log reservation deadlock
> vector between preallocated append transactions and transactions
> that are acquired at completion time for other purposes (i.e.,
> unwritten extent conversion or COW fork remaps). For example, if the
> ioend completion workqueue task executes on a batch of ioends that
> are sorted such that an append ioend sits at the tail, it's possible
> for the outstanding append transaction reservation to block
> allocation of transactions required to process preceding ioends in
> the list.
> 
> Append ioend completion is historically the common path for on-disk
> inode size updates. While file extending writes may have completed
> sometime earlier, the on-disk inode size is only updated after
> successful writeback completion. These transactions are preallocated
> serially from writeback context to mitigate concurrency and
> associated log reservation pressure across completions processed by
> multi-threaded workqueue tasks.
> 
> However, now that delalloc blocks unconditionally map to unwritten
> extents at physical block allocation time, size updates via append
> ioends are relatively rare. This means that inode size updates most
> commonly occur as part of the preexisting completion time
> transaction to convert unwritten extents. As a result, there is no
> longer a strong need to preallocate size update transactions.
> 
> Remove the preallocation of inode size update transactions to avoid
> the ioend completion processing log reservation deadlock. Instead,
> continue to send all potential size extending ioends to workqueue
> context for completion and allocate the transaction from that
> context. This ensures that no outstanding log reservation is owned
> by the ioend completion worker task when it begins to process
> ioends.
> 
> Signed-off-by: Brian Foster <bfoster@redhat.com>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> Reviewed-by: Darrick J. Wong <djwong@kernel.org>
> Signed-off-by: Darrick J. Wong <djwong@kernel.org>
> Reported-by: Christian Theune <ct@flyingcircus.io>
> Link: https://lore.kernel.org/linux-xfs/CAOQ4uxjj2UqA0h4Y31NbmpHksMhVrXfXjLG4Tnz3zq_UR-3gSA@mail.gmail.com/
> Signed-off-by: Amir Goldstein <amir73il@gmail.com>
> Acked-by: Darrick J. Wong <djwong@kernel.org>
> ---
> 
> Greg,
> 
> One more fix from v5.13 that I missed from my backports.

Now queued up, thanks.

greg k-h