Re: [PATCH 0/7] nfsd: filecache: change garbage collection lists

Chuck Lever
2025-02-06T14:35:57Z

On 2/5/25 10:04 PM, NeilBrown wrote:
> On Thu, 06 Feb 2025, Dave Chinner wrote:
>>
>> However, *every single shrinker implementation in the kernel* uses
>> this algorithm whether they use list-lru or not.
>
> Yes, but we aren't doing shrinking here. We are doing ageing.

The NFSD filecache uses this mechanism for both aging and shrinking.

What might be appropriate is to provide a list_lru API for aging. That
would have the benefit of using an existing common mechanism but make
it more appropriate for NFSD's usage scenario.

> We want
> a firm upper limit to how long things remain cached after the last use.

Do we need a firm limit? The age limit is not about correctness, is it?
What we don't want is a remote file access via NFSv3 to keep a file open
indefinitely. The current 2 second value is not a deep requirement, it's
merely a value that seems to work well.

That aspect is a little different than inode/dentry caching, where it
can be valuable (and at least, won't be harmful) to leave the item in
the cache.

--
Chuck Lever