On Wed, Apr 16, 2025 at 05:18:17PM +0200, Miklos Szeredi wrote:
> Lack of memory pressure should mean that nobody else needs that
> memory, so it should make no difference if it's used up in negative
> dentries instead of being free memory. Maybe I'm missing something
> fundamental?
You're missing two things:
- The dentry hash table is a fixed size. Long chains give poor
performance, so polluting the hash table with unused entries
has a cost.
- Eventually, we do trigger reclaim. And then we wait for hours while
the reclaiming process tries to shrink billions of entries. I think
we had a report on one machine of it taking more than 24 hours ("more
than" because the customer decided enough was enough and rebooted the
machine).
