Re: [PATCH 0/4] nfsd: filecache: change garbage collect lists

Chuck Lever
2025-01-22T19:22:31Z

On 1/21/25 10:54 PM, NeilBrown wrote:
>
> The nfsd filecache currently uses list_lru for tracking files recently
> used in NFSv3 requests which need to be "garbage collected" when they
> have becoming idle - unused for 2-4 seconds.
>
> I do not believe list_lru is a good tool for this. It does no allow the
> timeout which filecache requires so we have to add a timeout mechanism
> which holds the list_lru for while the whole list is scanned looking for
> entries that haven't been recently accessed. When the list is largish
> (even a few hundred) this can block new requests which need the lock to
> remove a file to access it.
>
> This patch removes the list_lru and instead uses 2 simple linked lists.
> When a file is accessed it is removed from whichever list it is one,
> then added to the tail of the first list. Every 2 seconds the second
> list is moved to the "freeme" list and the first list is moved to the
> second list. This avoids any need to walk a list to find old entries.
>
> These lists are per-netns rather than global as the freeme list is
> per-netns as the actual freeing is done in nfsd threads which are
> per-netns.
>
> This should not be applied until we resolve how to handle the
> race-detection code in nfsd_file_put(). However I'm posting it now to
> get any feedback so that a final version can be posted as soon as that
> issue is resolved.
>
> Thanks,
> NeilBrown
>
>
> [PATCH 1/4] nfsd: filecache: use nfsd_file_dispose_list() in
> [PATCH 2/4] nfsd: filecache: move globals nfsd_file_lru and
> [PATCH 3/4] nfsd: filecache: change garbage collection list
> [PATCH 4/4] nfsd: filecache: change garbage collection to a timer.

Hi Neil -

I would like Dave Chinner to chime in on this approach. When you
resend, please Cc: him. Thanks!

--
Chuck Lever