Re: [PATCH net] conntrack: perform a full scan in gc

Le 18/10/2016 à 10:47, Florian Westphal a écrit :

Nicolas Dichtel [off-list ref] wrote:

quoted

After commit b87a2f9199ea ("netfilter: conntrack: add gc worker to remove
timed-out entries"), netlink conntrack deletion events may be sent with a
huge delay (5 minutes).

There is two ways to evict conntrack:
 - during a conntrack lookup;
 - during a conntrack dump.
Let's do a full scan of conntrack entries after a period of inactivity
(no conntrack lookup).

CC: Florian Westphal <fw@strlen.de>
Signed-off-by: Nicolas Dichtel <redacted>
---

Here is another proposal to try to fix the problem.
Comments are welcomed,
Nicolas

Hmm, I don't think its good idea in practice.
If goal is to avoid starving arbitrary 'dead' ct for too long,
then simple ping will defeat the logic here, because...

quoted

 net/netfilter/nf_conntrack_core.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c
index ba6a1d421222..3dbb27bd9582 100644
--- a/net/netfilter/nf_conntrack_core.c
+++ b/net/netfilter/nf_conntrack_core.c

@@ -87,6 +87,7 @@ static __read_mostly bool nf_conntrack_locks_all;
 #define GC_MAX_BUCKETS		8192u
 #define GC_INTERVAL		(5 * HZ)
 #define GC_MAX_EVICTS		256u
+static bool gc_full_scan = true;
 
 static struct conntrack_gc_work conntrack_gc_work;
 

@@ -511,6 +512,7 @@ ____nf_conntrack_find(struct net *net, const struct nf_conntrack_zone *zone,
 	unsigned int bucket, hsize;
 
 begin:
+	gc_full_scan = false;

... we do periodic lookup (but always in same slot), so no full scan is
triggered.

Yes, I was wondering about that. My first idea was to have that bool per bucket
and force a scan of the bucket instead of the whole table.

If you think its useful, consider sending patch that rescheds worker
instantly in case budget expired, otherwise I will do this later this
week.

Ok, I will send it, but it does not address the "inactivity" problem.

[ I am aware doing instant restart might be too late, but at least we
  would then reap more entries once we stumble upon large number of
  expired ones ].