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

Message

NeilBrown Jan. 22, 2025, 3:54 a.m. UTC

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.