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authorSeongJae Park <sjpark@amazon.de>2020-12-11 14:24:05 +0300
committerJakub Kicinski <kuba@kernel.org>2020-12-13 02:08:54 +0300
commit0b9b241406818a871c6d25390aa487dba966d548 (patch)
tree8d1b4990106eed407ef7704833fe892584c37221
parente0a64d1dffca048a99546993322bd1fb5c728ee8 (diff)
downloadlinux-0b9b241406818a871c6d25390aa487dba966d548.tar.xz
inet: frags: batch fqdir destroy works
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>
-rw-r--r--include/net/inet_frag.h1
-rw-r--r--net/ipv4/inet_fragment.c47
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);