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![SeongJae Park](/assets/img/avatar_default.png)
On a few of our systems, I found frequent 'unshare(CLONE_NEWNET)' calls make the number of active slab objects including 'sock_inode_cache' type rapidly and continuously increase. As a result, memory pressure occurs. In more detail, I made an artificial reproducer that resembles the workload that we found the problem and reproduce the problem faster. It merely repeats 'unshare(CLONE_NEWNET)' 50,000 times in a loop. It takes about 2 minutes. On 40 CPU cores / 70GB DRAM machine, the available memory continuously reduced in a fast speed (about 120MB per second, 15GB in total within the 2 minutes). Note that the issue don't reproduce on every machine. On my 6 CPU cores machine, the problem didn't reproduce. 'cleanup_net()' and 'fqdir_work_fn()' are functions that deallocate the relevant memory objects. They are asynchronously invoked by the work queues and internally use 'rcu_barrier()' to ensure safe destructions. 'cleanup_net()' works in a batched maneer in a single thread worker, while 'fqdir_work_fn()' works for each 'fqdir_exit()' call in the 'system_wq'. Therefore, 'fqdir_work_fn()' called frequently under the workload and made the contention for 'rcu_barrier()' high. In more detail, the global mutex, 'rcu_state.barrier_mutex' became the bottleneck. This commit avoids such contention by doing the 'rcu_barrier()' and subsequent lightweight works in a batched manner, as similar to that of 'cleanup_net()'. The fqdir hashtable destruction, which is done before the 'rcu_barrier()', is still allowed to run in parallel for fast processing, but this commit makes it to use a dedicated work queue instead of the 'system_wq', to make sure that the number of threads is bounded. Signed-off-by: SeongJae Park <sjpark@amazon.de> Reviewed-by: Eric Dumazet <edumazet@google.com> Link: https://lore.kernel.org/r/20201211112405.31158-1-sjpark@amazon.com Signed-off-by: Jakub Kicinski <kuba@kernel.org>
178 lines
4.8 KiB
C
178 lines
4.8 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef __NET_FRAG_H__
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#define __NET_FRAG_H__
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#include <linux/rhashtable-types.h>
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#include <linux/completion.h>
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/* Per netns frag queues directory */
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struct fqdir {
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/* sysctls */
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long high_thresh;
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long low_thresh;
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int timeout;
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int max_dist;
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struct inet_frags *f;
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struct net *net;
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bool dead;
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struct rhashtable rhashtable ____cacheline_aligned_in_smp;
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/* Keep atomic mem on separate cachelines in structs that include it */
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atomic_long_t mem ____cacheline_aligned_in_smp;
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struct work_struct destroy_work;
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struct llist_node free_list;
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};
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/**
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* fragment queue flags
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*
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* @INET_FRAG_FIRST_IN: first fragment has arrived
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* @INET_FRAG_LAST_IN: final fragment has arrived
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* @INET_FRAG_COMPLETE: frag queue has been processed and is due for destruction
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* @INET_FRAG_HASH_DEAD: inet_frag_kill() has not removed fq from rhashtable
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*/
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enum {
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INET_FRAG_FIRST_IN = BIT(0),
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INET_FRAG_LAST_IN = BIT(1),
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INET_FRAG_COMPLETE = BIT(2),
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INET_FRAG_HASH_DEAD = BIT(3),
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};
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struct frag_v4_compare_key {
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__be32 saddr;
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__be32 daddr;
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u32 user;
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u32 vif;
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__be16 id;
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u16 protocol;
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};
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struct frag_v6_compare_key {
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struct in6_addr saddr;
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struct in6_addr daddr;
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u32 user;
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__be32 id;
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u32 iif;
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};
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/**
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* struct inet_frag_queue - fragment queue
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*
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* @node: rhash node
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* @key: keys identifying this frag.
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* @timer: queue expiration timer
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* @lock: spinlock protecting this frag
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* @refcnt: reference count of the queue
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* @rb_fragments: received fragments rb-tree root
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* @fragments_tail: received fragments tail
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* @last_run_head: the head of the last "run". see ip_fragment.c
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* @stamp: timestamp of the last received fragment
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* @len: total length of the original datagram
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* @meat: length of received fragments so far
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* @flags: fragment queue flags
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* @max_size: maximum received fragment size
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* @fqdir: pointer to struct fqdir
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* @rcu: rcu head for freeing deferall
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*/
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struct inet_frag_queue {
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struct rhash_head node;
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union {
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struct frag_v4_compare_key v4;
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struct frag_v6_compare_key v6;
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} key;
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struct timer_list timer;
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spinlock_t lock;
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refcount_t refcnt;
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struct rb_root rb_fragments;
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struct sk_buff *fragments_tail;
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struct sk_buff *last_run_head;
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ktime_t stamp;
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int len;
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int meat;
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__u8 flags;
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u16 max_size;
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struct fqdir *fqdir;
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struct rcu_head rcu;
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};
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struct inet_frags {
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unsigned int qsize;
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void (*constructor)(struct inet_frag_queue *q,
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const void *arg);
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void (*destructor)(struct inet_frag_queue *);
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void (*frag_expire)(struct timer_list *t);
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struct kmem_cache *frags_cachep;
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const char *frags_cache_name;
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struct rhashtable_params rhash_params;
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refcount_t refcnt;
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struct completion completion;
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};
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int inet_frags_init(struct inet_frags *);
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void inet_frags_fini(struct inet_frags *);
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int fqdir_init(struct fqdir **fqdirp, struct inet_frags *f, struct net *net);
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static inline void fqdir_pre_exit(struct fqdir *fqdir)
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{
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fqdir->high_thresh = 0; /* prevent creation of new frags */
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fqdir->dead = true;
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}
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void fqdir_exit(struct fqdir *fqdir);
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void inet_frag_kill(struct inet_frag_queue *q);
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void inet_frag_destroy(struct inet_frag_queue *q);
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struct inet_frag_queue *inet_frag_find(struct fqdir *fqdir, void *key);
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/* Free all skbs in the queue; return the sum of their truesizes. */
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unsigned int inet_frag_rbtree_purge(struct rb_root *root);
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static inline void inet_frag_put(struct inet_frag_queue *q)
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{
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if (refcount_dec_and_test(&q->refcnt))
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inet_frag_destroy(q);
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}
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/* Memory Tracking Functions. */
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static inline long frag_mem_limit(const struct fqdir *fqdir)
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{
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return atomic_long_read(&fqdir->mem);
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}
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static inline void sub_frag_mem_limit(struct fqdir *fqdir, long val)
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{
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atomic_long_sub(val, &fqdir->mem);
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}
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static inline void add_frag_mem_limit(struct fqdir *fqdir, long val)
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{
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atomic_long_add(val, &fqdir->mem);
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}
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/* RFC 3168 support :
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* We want to check ECN values of all fragments, do detect invalid combinations.
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* In ipq->ecn, we store the OR value of each ip4_frag_ecn() fragment value.
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*/
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#define IPFRAG_ECN_NOT_ECT 0x01 /* one frag had ECN_NOT_ECT */
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#define IPFRAG_ECN_ECT_1 0x02 /* one frag had ECN_ECT_1 */
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#define IPFRAG_ECN_ECT_0 0x04 /* one frag had ECN_ECT_0 */
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#define IPFRAG_ECN_CE 0x08 /* one frag had ECN_CE */
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extern const u8 ip_frag_ecn_table[16];
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/* Return values of inet_frag_queue_insert() */
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#define IPFRAG_OK 0
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#define IPFRAG_DUP 1
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#define IPFRAG_OVERLAP 2
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int inet_frag_queue_insert(struct inet_frag_queue *q, struct sk_buff *skb,
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int offset, int end);
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void *inet_frag_reasm_prepare(struct inet_frag_queue *q, struct sk_buff *skb,
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struct sk_buff *parent);
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void inet_frag_reasm_finish(struct inet_frag_queue *q, struct sk_buff *head,
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void *reasm_data, bool try_coalesce);
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struct sk_buff *inet_frag_pull_head(struct inet_frag_queue *q);
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#endif
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