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

NeilBrown
2025-01-27T01:23:14Z

[
davec added to cc incase I've said something incorrect about list_lru

Changes in this version:
- no _bh locking
- add name for a magic constant
- remove unnecessary race-handling code
- give a more meaningfule name for a lock for /proc/lock_stat
- minor cleanups suggested by Jeff

]

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 not allow
the timeout which filecache requires so we have to add a timeout
mechanism which holds the list_lru lock 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 noticably
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 on,
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.

Thanks,
NeilBrown

[PATCH 1/7] nfsd: filecache: remove race handling.
[PATCH 2/7] nfsd: filecache: use nfsd_file_dispose_list() in
[PATCH 3/7] nfsd: filecache: move globals nfsd_file_lru and
[PATCH 4/7] nfsd: filecache: change garbage collection list
[PATCH 5/7] nfsd: filecache: document the arbitrary limit on
[PATCH 6/7] nfsd: filecache: change garbage collection to a timer.
[PATCH 7/7] nfsd: filecache: give disposal lock a unique class name.