On Wed, 4 Dec 2013 05:54:57 -0800
Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote:
> > Yeah, I've noticed the same hang, but hadn't able to determine why it
> > was hanging. I suspect that that hang is what's tickles the bug that my
> > patch fixes. With the hang, we see the client doing retransmits and not
> > getting replies and that means that we exercise the DRC more...
>
> FYI here is the one that just kills the silly direct reclaim. It also
> fixes the oops, but I still see the hang:
>
>
> diff --git a/fs/nfsd/nfscache.c b/fs/nfsd/nfscache.c
> index 9186c7c..dd260a1 100644
> --- a/fs/nfsd/nfscache.c
> +++ b/fs/nfsd/nfscache.c
> @@ -380,11 +380,8 @@ nfsd_cache_search(struct svc_rqst *rqstp, __wsum csum)
> }
>
> /*
> - * Try to find an entry matching the current call in the cache. When none
> - * is found, we try to grab the oldest expired entry off the LRU list. If
> - * a suitable one isn't there, then drop the cache_lock and allocate a
> - * new one, then search again in case one got inserted while this thread
> - * didn't hold the lock.
> + * Try to find an entry matching the current call in the cache and if none is
> + * found allocate and insert a new one.
> */
> int
> nfsd_cache_lookup(struct svc_rqst *rqstp)
> @@ -409,22 +406,8 @@ nfsd_cache_lookup(struct svc_rqst *rqstp)
>
> /*
> * Since the common case is a cache miss followed by an insert,
> - * preallocate an entry. First, try to reuse the first entry on the LRU
> - * if it works, then go ahead and prune the LRU list.
> + * preallocate an entry.
> */
> - spin_lock(&cache_lock);
> - if (!list_empty(&lru_head)) {
> - rp = list_first_entry(&lru_head, struct svc_cacherep, c_lru);
> - if (nfsd_cache_entry_expired(rp) ||
> - num_drc_entries >= max_drc_entries) {
> - lru_put_end(rp);
> - prune_cache_entries();
> - goto search_cache;
> - }
> - }
> -
> - /* No expired ones available, allocate a new one. */
> - spin_unlock(&cache_lock);
> rp = nfsd_reply_cache_alloc();
> spin_lock(&cache_lock);
> if (likely(rp)) {
> @@ -432,7 +415,6 @@ nfsd_cache_lookup(struct svc_rqst *rqstp)
> drc_mem_usage += sizeof(*rp);
> }
>
It might be good to run prune_cache_entries(); at this point.
Otherwise, this looks like it'll be fine...
> -search_cache:
> found = nfsd_cache_search(rqstp, csum);
> if (found) {
> if (likely(rp))
> @@ -446,15 +428,6 @@ search_cache:
> goto out;
> }
>
> - /*
> - * We're keeping the one we just allocated. Are we now over the
> - * limit? Prune one off the tip of the LRU in trade for the one we
> - * just allocated if so.
> - */
> - if (num_drc_entries >= max_drc_entries)
> - nfsd_reply_cache_free_locked(list_first_entry(&lru_head,
> - struct svc_cacherep, c_lru));
> -
> nfsdstats.rcmisses++;
> rqstp->rq_cacherep = rp;
> rp->c_state = RC_INPROG;
--
Jeff Layton <jlayton@xxxxxxxxxx>
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