Re: [PATCH] mm: memcontrol: fix cgroup creation failure after many small jobs
From: Tejun Heo <tj@kernel.org>
Date: 2016-06-16 20:06:21
Also in:
linux-mm, lkml
Hello, Looks generally good to me. Some comments below. On Wed, Jun 15, 2016 at 11:42:44PM -0400, Johannes Weiner wrote:
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@@ -6205,6 +6205,24 @@ struct cgroup *cgroup_get_from_path(const char *path) } EXPORT_SYMBOL_GPL(cgroup_get_from_path); +/** + * css_id_free - relinquish an existing CSS's ID + * @css: the CSS + * + * This releases the @css's ID and allows it to be recycled while the + * CSS continues to exist. This is useful for controllers with state + * that extends past a cgroup's lifetime but doesn't need precious ID + * address space. + * + * This invalidates @css->id, and css_from_id() might return NULL or a + * new css if the ID has been recycled in the meantime. + */ +void css_id_free(struct cgroup_subsys_state *css) +{ + cgroup_idr_remove(&css->ss->css_idr, css->id); + css->id = 0; +}
I don't quite get why we're trying to free css->id earlier when memcg is gonna be using its private id anyway. From cgroup core side, the id space isn't restricted.
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diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 75e74408cc8f..1d8a6dffdc25 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c
...
+static void mem_cgroup_id_put(struct mem_cgroup *memcg)
+{
+ if (atomic_dec_and_test(&memcg->id.ref)) {
+ idr_remove(&mem_cgroup_idr, memcg->id.id);Maybe this should do "memcg->id.id = 0"?
+ css_id_free(&memcg->css);
+ css_put(&memcg->css);
+ }
+}
+
+/**
+ * mem_cgroup_from_id - look up a memcg from a memcg id
+ * @id: the memcg id to look up
+ *
+ * Caller must hold rcu_read_lock().
+ */
+struct mem_cgroup *mem_cgroup_from_id(unsigned short id)
+{
+ WARN_ON_ONCE(!rcu_read_lock_held());
+ return id > 0 ? idr_find(&mem_cgroup_idr, id) : NULL;
+}css_from_id() has it too but I don't think id > 0 test is necessary. We prolly should take it out of css_from_id() too. It might be useful to add comment explaining why memcg needs private ids. Thanks. -- tejun -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>