From: SeongJae Park <sjpark@xxxxxxxxx> 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@xxxxxxxxx> --- Changes from v3 (https://lore.kernel.org/lkml/20201211082032.26965-1-sjpark@xxxxxxxxxx/) - Use system_wq for the batched works and a dedicated non-ordered work queue for rhashtable destruction (Eric Dumazet) Changes from v2 (https://lore.kernel.org/lkml/20201210080844.23741-1-sjpark@xxxxxxxxxx/) - Add numbers after the patch (Eric Dumazet) - Make only 'rcu_barrier()' and subsequent lightweight works serialized (Eric Dumazet) Changes from v1 (https://lore.kernel.org/netdev/20201208094529.23266-1-sjpark@xxxxxxxxxx/) - Keep xmas tree variable ordering (Jakub Kicinski) - Add more numbers (Eric Dumazet) - Use 'llist_for_each_entry_safe()' (Eric Dumazet) --- include/net/inet_frag.h | 1 + net/ipv4/inet_fragment.c | 47 +++++++++++++++++++++++++++++++++------- 2 files changed, 40 insertions(+), 8 deletions(-) diff --git a/include/net/inet_frag.h b/include/net/inet_frag.h index bac79e817776..48cc5795ceda 100644 --- a/include/net/inet_frag.h +++ b/include/net/inet_frag.h @@ -21,6 +21,7 @@ struct fqdir { /* Keep atomic mem on separate cachelines in structs that include it */ atomic_long_t mem ____cacheline_aligned_in_smp; struct work_struct destroy_work; + struct llist_node free_list; }; /** diff --git a/net/ipv4/inet_fragment.c b/net/ipv4/inet_fragment.c index 10d31733297d..05cd198d7a6b 100644 --- a/net/ipv4/inet_fragment.c +++ b/net/ipv4/inet_fragment.c @@ -145,12 +145,16 @@ static void inet_frags_free_cb(void *ptr, void *arg) inet_frag_destroy(fq); } -static void fqdir_work_fn(struct work_struct *work) +static LLIST_HEAD(fqdir_free_list); + +static void fqdir_free_fn(struct work_struct *work) { - struct fqdir *fqdir = container_of(work, struct fqdir, destroy_work); - struct inet_frags *f = fqdir->f; + struct llist_node *kill_list; + struct fqdir *fqdir, *tmp; + struct inet_frags *f; - rhashtable_free_and_destroy(&fqdir->rhashtable, inet_frags_free_cb, NULL); + /* Atomically snapshot the list of fqdirs to free */ + kill_list = llist_del_all(&fqdir_free_list); /* We need to make sure all ongoing call_rcu(..., inet_frag_destroy_rcu) * have completed, since they need to dereference fqdir. @@ -158,10 +162,25 @@ static void fqdir_work_fn(struct work_struct *work) */ rcu_barrier(); - if (refcount_dec_and_test(&f->refcnt)) - complete(&f->completion); + llist_for_each_entry_safe(fqdir, tmp, kill_list, free_list) { + f = fqdir->f; + if (refcount_dec_and_test(&f->refcnt)) + complete(&f->completion); - kfree(fqdir); + kfree(fqdir); + } +} + +static DECLARE_WORK(fqdir_free_work, fqdir_free_fn); + +static void fqdir_work_fn(struct work_struct *work) +{ + struct fqdir *fqdir = container_of(work, struct fqdir, destroy_work); + + rhashtable_free_and_destroy(&fqdir->rhashtable, inet_frags_free_cb, NULL); + + if (llist_add(&fqdir->free_list, &fqdir_free_list)) + queue_work(system_wq, &fqdir_free_work); } int fqdir_init(struct fqdir **fqdirp, struct inet_frags *f, struct net *net) @@ -184,10 +203,22 @@ int fqdir_init(struct fqdir **fqdirp, struct inet_frags *f, struct net *net) } EXPORT_SYMBOL(fqdir_init); +static struct workqueue_struct *inet_frag_wq; + +static int __init inet_frag_wq_init(void) +{ + inet_frag_wq = create_workqueue("inet_frag_wq"); + if (!inet_frag_wq) + panic("Could not create inet frag workq"); + return 0; +} + +pure_initcall(inet_frag_wq_init); + void fqdir_exit(struct fqdir *fqdir) { INIT_WORK(&fqdir->destroy_work, fqdir_work_fn); - queue_work(system_wq, &fqdir->destroy_work); + queue_work(inet_frag_wq, &fqdir->destroy_work); } EXPORT_SYMBOL(fqdir_exit); -- 2.17.1