Re: [PATCH 4/4] xfs: don't decrement the buffer LRU count for in-use buffers

[Dave Chinner <dgc@kernel.org>]

On Tue, Mar 17, 2026 at 02:40:55PM +0100, Christoph Hellwig wrote:
> XFS buffers are added to the LRU when they are unused, but are only
> removed from the LRU lazily when the LRU list scan finds a used buffer.
> So far this only happen when the LRU counter hits 0, which is suboptimal
> as buffers that were added to the LRU, but are in use again still consume
> LRU scanning resources and are aged while actually in use.
> 
> Fix this by checking for in-use buffers and removing the from the LRU
> before decrementing the LRU counter.

So I wondered why you put the "in use" check where you did a couple
of patches ago - it didn't make a lot of sense to me because 'in use
buffers' typically reset the lru count to their maximum at the same
time they lookup, lock and take a reference to the buffer. The the
lock and reference are dropped at the same time when we are done
with the buffer, so it never made sense to decrement the LRU count
whilst buffers are locked and referenced...

Can you just fold this back into the original patch that introduces
this check?

-Dave.
-- 
Dave Chinner
dgc@kernel.org