linux-kernel - [PATCH v2] livepatch: Reduce the time of finding module symbols

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Message-ID: <1490706635-45752-1-git-send-email-zhouchengming1@huawei.com>
Date:   Tue, 28 Mar 2017 21:10:35 +0800
From:   Zhou Chengming <zhouchengming1@...wei.com>
To:     <live-patching@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC:     <jpoimboe@...hat.com>, <jeyu@...hat.com>, <jikos@...nel.org>,
        <mbenes@...e.cz>, <pmladek@...e.com>, <huawei.libin@...wei.com>,
        <zhouchengming1@...wei.com>
Subject: [PATCH v2] livepatch: Reduce the time of finding module symbols

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 <zhouchengming1@...wei.com>
---
 kernel/livepatch/core.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index af46438..b4b8bb0 100644
--- 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);

 	/*
-- 
1.8.3.1