Re: [PATCH] nfsd: when reusing an existing repcache entry, unhash it first

[Christoph Hellwig <hch@infradead.org>]

On Tue, Dec 03, 2013 at 01:21:12PM -0500, Jeff Layton wrote:
> Most of this code is protected by a single spinlock (cache_lock). The
> main benefit to switching to list_lru would be that we could move to a
> per-node lock. But, to make that worthwhile would mean we'd need to
> redesign the locking and break the cache_lock into multiple locks.

No need to redo locks just yet, the biggest benefit is to use a well
debug library for lru list handling, with the second biggest one being
that you get out of the box shrinker support.

> Also, the existing code does take pains to reuse an expired entry off
> the LRU list in preference to allocating a new one. The list_lru code
> doesn't have a mechanism to scrape the first entry off the LRU list,
> though I suppose we could add one or abuse the cb_arg in the walk
> callback as a return pointer.

That's just because it is an old-school cache with a fixed upper bound
of entries and no shrinker support.  With proper shrinker integration
this nasty code isn't needed.