linux-kernel - Re: module: Optimize search_module

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Date:   Fri, 10 Feb 2017 23:41:34 -0500
From:   Jessica Yu <jeyu@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     rusty@...tcorp.com.au, Mark Rutland <mark.rutland@....com>,
        linux-kernel@...r.kernel.org
Subject: Re: module: Optimize search_module_extables()

+++ Peter Zijlstra [08/02/17 15:48 +0100]:
>
>While looking through the __ex_table stuff I found that we do a linear
>lookup of the module. Also fix up a comment.
>
>Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>

Applied, thanks.

Hm. A quick scan through module.c still shows a couple of places that use
similar linear lookups, and may benefit from the same __module_address
optimization. But I'll save that for a separate patch..

Jessica

>---
> kernel/module.c | 27 ++++++++++++++-------------
> 1 file changed, 14 insertions(+), 13 deletions(-)
>
>diff --git a/kernel/module.c b/kernel/module.c
>index 3d8f126208e3..7bcdc35dbf95 100644
>--- a/kernel/module.c
>+++ b/kernel/module.c
>@@ -4165,22 +4165,23 @@ const struct exception_table_entry *search_module_extables(unsigned long addr)
> 	struct module *mod;
>
> 	preempt_disable();
>-	list_for_each_entry_rcu(mod, &modules, list) {
>-		if (mod->state == MODULE_STATE_UNFORMED)
>-			continue;
>-		if (mod->num_exentries == 0)
>-			continue;
>+	mod = __module_address(addr);
>+	if (!mod)
>+		goto out;
>
>-		e = search_extable(mod->extable,
>-				   mod->extable + mod->num_exentries - 1,
>-				   addr);
>-		if (e)
>-			break;
>-	}
>+	if (!mod->num_exentries)
>+		goto out;
>+
>+	e = search_extable(mod->extable,
>+			   mod->extable + mod->num_exentries - 1,
>+			   addr);
>+out:
> 	preempt_enable();
>
>-	/* Now, if we found one, we are running inside it now, hence
>-	   we cannot unload the module, hence no refcnt needed. */
>+	/*
>+	 * Now, if we found one, we are running inside it now, hence
>+	 * we cannot unload the module, hence no refcnt needed.
>+	 */
> 	return e;
> }
>