Re: [PATCH] loop: add WQ_MEM_RECLAIM flag to per device workqueue

[Tejun Heo <tj@kernel.org>]

Hello,

On Wed, Mar 23, 2022 at 09:00:07AM +1100, Dave Chinner wrote:
> > Yeah, you detected multiple issues at the same time. xfs sync is
> > participating in memory reclaim
> 
> No it isn't. What makes you think it is part of memory reclaim?
> 
> The xfs-sync workqueue exists solely to perform async flushes of
> dirty data at ENOSPC via sync_inodes_sb() because we can't call
> sync_inodes_sb directly in the context that hit ENOSPC due to locks
> and transaction contexts held. The paths that need this are
> buffered writes and file create (on disk inode allocation), neither
> of which are in the the memory reclaim path, either.
> 
> So this work has nothing to do with memory reclaim, and as such it's
> not tagged with WQ_MEM_RECLAIM.

Hmmm... yeah, I actually don't know the exact dependency here and the
dependency may not be real - e.g. the conclusion might be that loop is
conflating different uses and needs to split its use of workqueues into two
separate ones. Tetsuo, can you post more details on the warning that you're
seeing?

Thanks.

-- 
tejun