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Subject[PATCH v5 07/10] module: Optimize __module_address() using a latched RB-tree
Currently __module_address() is using a linear search through all
modules in order to find the module corresponding to the provided
address. With a lot of modules this can take a lot of time.

One of the users of this is kernel_text_address() which is employed
in many stack unwinders; which in turn are used by perf-callchain and
ftrace (possibly from NMI context).

So by optimizing __module_address() we optimize many stack unwinders
which are used by both perf and tracing in performance sensitive code.

Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
include/linux/module.h | 29 ++++++++++--
kernel/module.c | 117 ++++++++++++++++++++++++++++++++++++++++++++++---
2 files changed, 138 insertions(+), 8 deletions(-)

--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -17,6 +17,7 @@
#include <linux/moduleparam.h>
#include <linux/jump_label.h>
#include <linux/export.h>
+#include <linux/rbtree_latch.h>

#include <linux/percpu.h>
#include <asm/module.h>
@@ -210,6 +211,13 @@ enum module_state {
MODULE_STATE_UNFORMED, /* Still setting it up. */
};

+struct module;
+
+struct mod_tree_node {
+ struct module *mod;
+ struct latch_tree_node node;
+};
+
struct module {
enum module_state state;

@@ -269,8 +277,15 @@ struct module {
/* Startup function. */
int (*init)(void);

- /* If this is non-NULL, vfree after init() returns */
- void *module_init;
+ /*
+ * If this is non-NULL, vfree after init() returns.
+ *
+ * Cacheline align here, such that:
+ * module_init, module_core, init_size, core_size,
+ * init_text_size, core_text_size and ltn_core.node[0]
+ * are on the same cacheline.
+ */
+ void *module_init ____cacheline_aligned;

/* Here is the actual code + data, vfree'd on unload. */
void *module_core;
@@ -281,6 +296,14 @@ struct module {
/* The size of the executable code in each section. */
unsigned int init_text_size, core_text_size;

+ /*
+ * We want mtn_core::{mod,node[0]} to be in the same cacheline as the
+ * above entries such that a regular lookup will only touch the one
+ * cacheline.
+ */
+ struct mod_tree_node mtn_core;
+ struct mod_tree_node mtn_init;
+
/* Size of RO sections of the module (text+rodata) */
unsigned int init_ro_size, core_ro_size;

@@ -365,7 +388,7 @@ struct module {
ctor_fn_t *ctors;
unsigned int num_ctors;
#endif
-};
+} ____cacheline_aligned;
#ifndef MODULE_ARCH_INIT
#define MODULE_ARCH_INIT {}
#endif
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -101,6 +101,109 @@
DEFINE_MUTEX(module_mutex);
EXPORT_SYMBOL_GPL(module_mutex);
static LIST_HEAD(modules);
+
+/*
+ * Use a latched RB-tree for __module_address(); this allows us to use
+ * RCU-sched lookups of the address from any context.
+ *
+ * Because modules have two address ranges: init and core, we need two
+ * latch_tree_nodes entries. Therefore we need the back-pointer from
+ * mod_tree_node.
+ *
+ * Because init ranges are short lived we mark them unlikely and have placed
+ * them outside the critical cacheline in struct module.
+ */
+
+static __always_inline unsigned long __mod_tree_val(struct latch_tree_node *n)
+{
+ struct mod_tree_node *mtn = container_of(n, struct mod_tree_node, node);
+ struct module *mod = mtn->mod;
+
+ if (unlikely(mtn == &mod->mtn_init))
+ return (unsigned long)mod->module_init;
+
+ return (unsigned long)mod->module_core;
+}
+
+static __always_inline unsigned long __mod_tree_size(struct latch_tree_node *n)
+{
+ struct mod_tree_node *mtn = container_of(n, struct mod_tree_node, node);
+ struct module *mod = mtn->mod;
+
+ if (unlikely(mtn == &mod->mtn_init))
+ return (unsigned long)mod->init_size;
+
+ return (unsigned long)mod->core_size;
+}
+
+static __always_inline bool
+mod_tree_less(struct latch_tree_node *a, struct latch_tree_node *b)
+{
+ return __mod_tree_val(a) < __mod_tree_val(b);
+}
+
+static __always_inline int
+mod_tree_comp(void *key, struct latch_tree_node *n)
+{
+ unsigned long val = (unsigned long)key;
+ unsigned long start, end;
+
+ end = start = __mod_tree_val(n);
+ end += __mod_tree_size(n);
+
+ if (val < start)
+ return -1;
+
+ if (val >= end)
+ return 1;
+
+ return 0;
+}
+
+static const struct latch_tree_ops mod_tree_ops = {
+ .less = mod_tree_less,
+ .comp = mod_tree_comp,
+};
+
+static struct latch_tree_root mod_tree __cacheline_aligned;
+
+/*
+ * These modifications: insert, remove_init and remove; are serialized by the
+ * module_mutex.
+ */
+static void mod_tree_insert(struct module *mod)
+{
+ mod->mtn_core.mod = mod;
+ mod->mtn_init.mod = mod;
+
+ latch_tree_insert(&mod->mtn_core.node, &mod_tree, &mod_tree_ops);
+ if (mod->init_size)
+ latch_tree_insert(&mod->mtn_init.node, &mod_tree, &mod_tree_ops);
+}
+
+static void mod_tree_remove_init(struct module *mod)
+{
+ if (mod->init_size)
+ latch_tree_erase(&mod->mtn_init.node, &mod_tree, &mod_tree_ops);
+}
+
+static void mod_tree_remove(struct module *mod)
+{
+ latch_tree_erase(&mod->mtn_core.node, &mod_tree, &mod_tree_ops);
+ mod_tree_remove_init(mod);
+}
+
+static struct module *mod_tree_find(unsigned long addr)
+{
+ struct latch_tree_node *ltn;
+
+ ltn = latch_tree_find((void *)addr, &mod_tree, &mod_tree_ops);
+ if (!ltn)
+ return NULL;
+
+ return container_of(ltn, struct mod_tree_node, node)->mod;
+}
+
#ifdef CONFIG_KGDB_KDB
struct list_head *kdb_modules = &modules; /* kdb needs the list of modules */
#endif /* CONFIG_KGDB_KDB */
@@ -1880,6 +1983,7 @@ static void free_module(struct module *m
mutex_lock(&module_mutex);
/* Unlink carefully: kallsyms could be walking list. */
list_del_rcu(&mod->list);
+ mod_tree_remove(mod);
/* Remove this module from bug list, this uses list_del_rcu */
module_bug_cleanup(mod);
/* Wait for RCU-sched synchronizing before releasing mod->list and buglist. */
@@ -3126,6 +3230,7 @@ static noinline int do_init_module(struc
mod->symtab = mod->core_symtab;
mod->strtab = mod->core_strtab;
#endif
+ mod_tree_remove_init(mod);
unset_module_init_ro_nx(mod);
module_arch_freeing_init(mod);
mod->module_init = NULL;
@@ -3196,6 +3301,7 @@ static int add_unformed_module(struct mo
goto out;
}
list_add_rcu(&mod->list, &modules);
+ mod_tree_insert(mod);
err = 0;

out:
@@ -3395,6 +3501,7 @@ static int load_module(struct load_info
mutex_lock(&module_mutex);
/* Unlink carefully: kallsyms could be walking list. */
list_del_rcu(&mod->list);
+ mod_tree_remove(mod);
wake_up_all(&module_wq);
/* Wait for RCU-sched synchronizing before releasing mod->list. */
synchronize_sched();
@@ -3842,13 +3949,13 @@ struct module *__module_address(unsigned

module_assert_mutex_or_preempt();

- list_for_each_entry_rcu(mod, &modules, list) {
+ mod = mod_tree_find(addr);
+ if (mod) {
+ BUG_ON(!within_module(addr, mod));
if (mod->state == MODULE_STATE_UNFORMED)
- continue;
- if (within_module(addr, mod))
- return mod;
+ mod = NULL;
}
- return NULL;
+ return mod;
}
EXPORT_SYMBOL_GPL(__module_address);




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