[3.11.y.z extended stable] Patch "nfsd: don't try to reuse an expired DRC entry off the list" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    nfsd: don't try to reuse an expired DRC entry off the list

to the linux-3.11.y-queue branch of the 3.11.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.11.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.11.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 9696a6f0ee3a1ea18b9b705a70eb76883cebe7a0 Mon Sep 17 00:00:00 2001
From: Jeff Layton <jlayton at redhat.com>
Date: Thu, 5 Dec 2013 06:00:51 -0500
Subject: nfsd: don't try to reuse an expired DRC entry off the list

commit a0ef5e19684f0447da9ff0654a12019c484f57ca upstream.

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 at redhat.com>
Signed-off-by: J. Bruce Fields <bfields at redhat.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 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;
--
1.9.1