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authorJesper Dangaard Brouer <brouer@redhat.com>2017-09-01 11:26:08 +0200
committerDavid S. Miller <davem@davemloft.net>2017-09-03 11:01:05 -0700
commitfb452a1aa3fd4034d7999e309c5466ff2d7005aa (patch)
tree929f2e7692f05a685de60535e2de27aa37579400 /include/net/inet_frag.h
parent64327fc811268d4a24de03dac242ea29de6be75f (diff)
Revert "net: use lib/percpu_counter API for fragmentation mem accounting"
This reverts commit 6d7b857d541ecd1d9bd997c97242d4ef94b19de2. There is a bug in fragmentation codes use of the percpu_counter API, that can cause issues on systems with many CPUs. The frag_mem_limit() just reads the global counter (fbc->count), without considering other CPUs can have upto batch size (130K) that haven't been subtracted yet. Due to the 3MBytes lower thresh limit, this become dangerous at >=24 CPUs (3*1024*1024/130000=24). The correct API usage would be to use __percpu_counter_compare() which does the right thing, and takes into account the number of (online) CPUs and batch size, to account for this and call __percpu_counter_sum() when needed. We choose to revert the use of the lib/percpu_counter API for frag memory accounting for several reasons: 1) On systems with CPUs > 24, the heavier fully locked __percpu_counter_sum() is always invoked, which will be more expensive than the atomic_t that is reverted to. Given systems with more than 24 CPUs are becoming common this doesn't seem like a good option. To mitigate this, the batch size could be decreased and thresh be increased. 2) The add_frag_mem_limit+sub_frag_mem_limit pairs happen on the RX CPU, before SKBs are pushed into sockets on remote CPUs. Given NICs can only hash on L2 part of the IP-header, the NIC-RXq's will likely be limited. Thus, a fair chance that atomic add+dec happen on the same CPU. Revert note that commit 1d6119baf061 ("net: fix percpu memory leaks") removed init_frag_mem_limit() and instead use inet_frags_init_net(). After this revert, inet_frags_uninit_net() becomes empty. Fixes: 6d7b857d541e ("net: use lib/percpu_counter API for fragmentation mem accounting") Fixes: 1d6119baf061 ("net: fix percpu memory leaks") Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com> Acked-by: Florian Westphal <fw@strlen.de> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'include/net/inet_frag.h')
-rw-r--r--include/net/inet_frag.h30
1 files changed, 9 insertions, 21 deletions
diff --git a/include/net/inet_frag.h b/include/net/inet_frag.h
index 6fdcd2427776..fa635aa6d0b9 100644
--- a/include/net/inet_frag.h
+++ b/include/net/inet_frag.h
@@ -1,14 +1,9 @@
#ifndef __NET_FRAG_H__
#define __NET_FRAG_H__
-#include <linux/percpu_counter.h>
-
struct netns_frags {
- /* The percpu_counter "mem" need to be cacheline aligned.
- * mem.count must not share cacheline with other writers
- */
- struct percpu_counter mem ____cacheline_aligned_in_smp;
-
+ /* Keep atomic mem on separate cachelines in structs that include it */
+ atomic_t mem ____cacheline_aligned_in_smp;
/* sysctls */
int timeout;
int high_thresh;
@@ -110,11 +105,11 @@ void inet_frags_fini(struct inet_frags *);
static inline int inet_frags_init_net(struct netns_frags *nf)
{
- return percpu_counter_init(&nf->mem, 0, GFP_KERNEL);
+ atomic_set(&nf->mem, 0);
+ return 0;
}
static inline void inet_frags_uninit_net(struct netns_frags *nf)
{
- percpu_counter_destroy(&nf->mem);
}
void inet_frags_exit_net(struct netns_frags *nf, struct inet_frags *f);
@@ -140,31 +135,24 @@ static inline bool inet_frag_evicting(struct inet_frag_queue *q)
/* Memory Tracking Functions. */
-/* The default percpu_counter batch size is not big enough to scale to
- * fragmentation mem acct sizes.
- * The mem size of a 64K fragment is approx:
- * (44 fragments * 2944 truesize) + frag_queue struct(200) = 129736 bytes
- */
-static unsigned int frag_percpu_counter_batch = 130000;
-
static inline int frag_mem_limit(struct netns_frags *nf)
{
- return percpu_counter_read(&nf->mem);
+ return atomic_read(&nf->mem);
}
static inline void sub_frag_mem_limit(struct netns_frags *nf, int i)
{
- percpu_counter_add_batch(&nf->mem, -i, frag_percpu_counter_batch);
+ atomic_sub(i, &nf->mem);
}
static inline void add_frag_mem_limit(struct netns_frags *nf, int i)
{
- percpu_counter_add_batch(&nf->mem, i, frag_percpu_counter_batch);
+ atomic_add(i, &nf->mem);
}
-static inline unsigned int sum_frag_mem_limit(struct netns_frags *nf)
+static inline int sum_frag_mem_limit(struct netns_frags *nf)
{
- return percpu_counter_sum_positive(&nf->mem);
+ return atomic_read(&nf->mem);
}
/* RFC 3168 support :