From: SeongJae Park <sjp...@amazon.de>
For each 'fqdir_exit()' call, a work for destroy of the 'fqdir' is
enqueued. The work function, 'fqdir_work_fn()', internally calls
'rcu_barrier()'. In case of intensive 'fqdir_exit()' (e.g., frequent
'unshare()' systemcalls), this increased contention could result in
unacceptably high latency of 'rcu_barrier()'. This commit avoids such
contention by doing the 'rcu_barrier()' and subsequent lightweight works
in a batched manner using a dedicated singlethread worker, as similar to
that of 'cleanup_net()'.
Signed-off-by: SeongJae Park <sjp...@amazon.de>
---
include/net/inet_frag.h | 1 +
net/ipv4/inet_fragment.c | 45 +++++++++++++++++++++++++++++++++-------
2 files changed, 39 insertions(+), 7 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..a6fc4afcc323 100644
--- a/net/ipv4/inet_fragment.c
+++ b/net/ipv4/inet_fragment.c
@@ -145,12 +145,17 @@ static void inet_frags_free_cb(void *ptr, void *arg)
inet_frag_destroy(fq);
}
-static void fqdir_work_fn(struct work_struct *work)
+static struct workqueue_struct *fqdir_wq;
+static LLIST_HEAD(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(&free_list);
/* We need to make sure all ongoing call_rcu(..., inet_frag_destroy_rcu)
* have completed, since they need to dereference fqdir.
@@ -158,12 +163,38 @@ 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, &free_list))
+ queue_work(fqdir_wq, &fqdir_free_work);
+}
+
+static int __init fqdir_wq_init(void)
+{
+ fqdir_wq = create_singlethread_workqueue("fqdir");
+ if (!fqdir_wq)
+ panic("Could not create fqdir workq");
+ return 0;
+}
+
+pure_initcall(fqdir_wq_init);
+
+
int fqdir_init(struct fqdir **fqdirp, struct inet_frags *f, struct net *net)
{
struct fqdir *fqdir = kzalloc(sizeof(*fqdir), GFP_KERNEL);
--
2.17.1
