livepatch: Reduce the time of finding module symbols

zhouchengming1 · Jiri Kosina · commit 72f04b50d61c · 2017-03-30T10:41:38.000+02:00
It's reported that the time of insmoding a klp.ko for one of our
out-tree modules is too long.

~ time sudo insmod klp.ko
real	0m23.799s
user	0m0.036s
sys	0m21.256s

Then we found the reason: our out-tree module used a lot of static local
variables, so klp.ko has a lot of relocation records which reference the
module. Then for each such entry klp_find_object_symbol() is called to
resolve it, but this function uses the interface kallsyms_on_each_symbol()
even for finding module symbols, so will waste a lot of time on walking
through vmlinux kallsyms table many times.

This patch changes it to use module_kallsyms_on_each_symbol() for modules
symbols. After we apply this patch, the sys time reduced dramatically.

~ time sudo insmod klp.ko
real	0m1.007s
user	0m0.032s
sys	0m0.924s

Signed-off-by: Zhou Chengming &lt;zhouchengming1@huawei.com&gt;
Acked-by: Josh Poimboeuf &lt;jpoimboe@redhat.com&gt;
Acked-by: Jessica Yu &lt;jeyu@redhat.com&gt;
Acked-by: Miroslav Benes &lt;mbenes@suse.cz&gt;
Signed-off-by: Jiri Kosina &lt;jkosina@suse.cz&gt;
diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
@@ -182,7 +182,10 @@ static int klp_find_object_symbol(const char *objname, const char *name,
 	};
 
 	mutex_lock(&module_mutex);
-	kallsyms_on_each_symbol(klp_find_callback, &args);
+	if (objname)
+		module_kallsyms_on_each_symbol(klp_find_callback, &args);
+	else
+		kallsyms_on_each_symbol(klp_find_callback, &args);
 	mutex_unlock(&module_mutex);
 
 	/*
