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

[NeilBrown <neilb@suse.de>]

[
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.