Thanks, Jeff.
Acked-by: J. Bruce Fields <bfields@xxxxxxxxxx>
--b.
On Fri, Jun 20, 2014 at 02:56:52PM -0400, Jeff Layton wrote:
> From: Jeff Layton <jlayton@xxxxxxxxxx>
>
> This is commit a0ef5e19684f0447da9ff0654a12019c484f57ca in mainline.
>
> While the commit message below doesn't lay this out, we've subsequently
> found that there are some cases where an entry that's still in use can
> be freed prematurely if a particular operation takes a *very* long time
> (on the order of minutes) and/or the server is very busy and doesn't
> have a lot of memory dedicated to the DRC. This patch eliminates that
> possibility, so it's actually more than just a cleanup.
>
> The regression crept in in v3.9, and this patch went into mainline in
> v3.14. Please apply this to any stable kernel between those two
> mainline releases.
>
> Original patch description follows:
>
> -------------------------------[snip]----------------------------
>
> Currently when we are processing a request, we try to scrape an expired
> or over-limit entry off the list in preference to allocating a new one
> from the slab.
>
> This is unnecessarily complicated. Just use the slab layer.
>
> Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
> Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx>
> ---
> fs/nfsd/nfscache.c | 36 ++++--------------------------------
> 1 file changed, 4 insertions(+), 32 deletions(-)
>
> diff --git a/fs/nfsd/nfscache.c b/fs/nfsd/nfscache.c
> index ec8d97ddc635..02e8e9ad5750 100644
> --- a/fs/nfsd/nfscache.c
> +++ b/fs/nfsd/nfscache.c
> @@ -129,13 +129,6 @@ nfsd_reply_cache_alloc(void)
> }
>
> static void
> -nfsd_reply_cache_unhash(struct svc_cacherep *rp)
> -{
> - hlist_del_init(&rp->c_hash);
> - list_del_init(&rp->c_lru);
> -}
> -
> -static void
> nfsd_reply_cache_free_locked(struct svc_cacherep *rp)
> {
> if (rp->c_type == RC_REPLBUFF && rp->c_replvec.iov_base) {
> @@ -402,22 +395,8 @@ 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) {
> - nfsd_reply_cache_unhash(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)) {
> @@ -425,7 +404,9 @@ nfsd_cache_lookup(struct svc_rqst *rqstp)
> drc_mem_usage += sizeof(*rp);
> }
>
> -search_cache:
> + /* go ahead and prune the cache */
> + prune_cache_entries();
> +
> found = nfsd_cache_search(rqstp, csum);
> if (found) {
> if (likely(rp))
> @@ -439,15 +420,6 @@ 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;
> --
> 1.9.3
>
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