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Revert "net: use lib/percpu_counter API for fragmentation mem accounting"
This reverts commit6d7b857d54
. 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 commit1d6119baf0
("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:6d7b857d54
("net: use lib/percpu_counter API for fragmentation mem accounting") Fixes:1d6119baf0
("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>
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@ -1,14 +1,9 @@
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#ifndef __NET_FRAG_H__
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#define __NET_FRAG_H__
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#include <linux/percpu_counter.h>
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struct netns_frags {
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/* The percpu_counter "mem" need to be cacheline aligned.
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* mem.count must not share cacheline with other writers
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*/
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struct percpu_counter mem ____cacheline_aligned_in_smp;
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/* Keep atomic mem on separate cachelines in structs that include it */
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atomic_t mem ____cacheline_aligned_in_smp;
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/* sysctls */
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int timeout;
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int high_thresh;
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@ -110,11 +105,11 @@ void inet_frags_fini(struct inet_frags *);
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static inline int inet_frags_init_net(struct netns_frags *nf)
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{
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return percpu_counter_init(&nf->mem, 0, GFP_KERNEL);
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atomic_set(&nf->mem, 0);
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return 0;
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}
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static inline void inet_frags_uninit_net(struct netns_frags *nf)
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{
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percpu_counter_destroy(&nf->mem);
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}
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void inet_frags_exit_net(struct netns_frags *nf, struct inet_frags *f);
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@ -140,31 +135,24 @@ static inline bool inet_frag_evicting(struct inet_frag_queue *q)
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/* Memory Tracking Functions. */
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/* The default percpu_counter batch size is not big enough to scale to
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* fragmentation mem acct sizes.
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* The mem size of a 64K fragment is approx:
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* (44 fragments * 2944 truesize) + frag_queue struct(200) = 129736 bytes
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*/
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static unsigned int frag_percpu_counter_batch = 130000;
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static inline int frag_mem_limit(struct netns_frags *nf)
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{
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return percpu_counter_read(&nf->mem);
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return atomic_read(&nf->mem);
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}
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static inline void sub_frag_mem_limit(struct netns_frags *nf, int i)
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{
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percpu_counter_add_batch(&nf->mem, -i, frag_percpu_counter_batch);
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atomic_sub(i, &nf->mem);
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}
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static inline void add_frag_mem_limit(struct netns_frags *nf, int i)
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{
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percpu_counter_add_batch(&nf->mem, i, frag_percpu_counter_batch);
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atomic_add(i, &nf->mem);
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}
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static inline unsigned int sum_frag_mem_limit(struct netns_frags *nf)
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static inline int sum_frag_mem_limit(struct netns_frags *nf)
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{
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return percpu_counter_sum_positive(&nf->mem);
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return atomic_read(&nf->mem);
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}
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/* RFC 3168 support :
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@ -234,10 +234,8 @@ evict_again:
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cond_resched();
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if (read_seqretry(&f->rnd_seqlock, seq) ||
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percpu_counter_sum(&nf->mem))
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sum_frag_mem_limit(nf))
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goto evict_again;
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percpu_counter_destroy(&nf->mem);
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}
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EXPORT_SYMBOL(inet_frags_exit_net);
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