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Commit 93c2e105 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Rusty Russell
Browse files

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: Rusty Russell <rusty@rustcorp.com.au>
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>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
parent ade3f510

include/linux/module.h

+26 −3
Original line number Diff line number Diff line
@@ -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 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;
@@ -367,7 +390,7 @@ struct module { 
	ctor_fn_t *ctors;

	unsigned int num_ctors;

#endif

};

} ____cacheline_aligned;

#ifndef MODULE_ARCH_INIT

#define MODULE_ARCH_INIT {}

#endif

kernel/module.c

+110 −5
Original line number Diff line number Diff line
@@ -101,6 +101,108 @@ 
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;



	start = __mod_tree_val(n);

	if (val < start)

		return -1;



	end = start + __mod_tree_size(n);

	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 */
@@ -1878,6 +1980,7 @@ static void free_module(struct module *mod) 
	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. */
@@ -3145,6 +3248,7 @@ static noinline int do_init_module(struct module *mod) 
	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;
@@ -3215,6 +3319,7 @@ static int add_unformed_module(struct module *mod) 
		goto out;

	}

	list_add_rcu(&mod->list, &modules);

	mod_tree_insert(mod);

	err = 0;



out:
@@ -3861,13 +3966,13 @@ struct module *__module_address(unsigned long addr) 


	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);