linux-kernel - Re: [PATCH 1/3] livepatch: Improve the search performance of module_kallsyms_on_each

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Date:   Wed, 4 Jan 2023 16:36:28 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Zhen Lei <thunder.leizhen@...wei.com>
Cc:     Josh Poimboeuf <jpoimboe@...nel.org>,
        Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mark Rutland <mark.rutland@....com>, bpf@...r.kernel.org,
        linux-trace-kernel@...r.kernel.org, live-patching@...r.kernel.org,
        linux-kernel@...r.kernel.org, Luis Chamberlain <mcgrof@...nel.org>,
        linux-modules@...r.kernel.org
Subject: Re: [PATCH 1/3] livepatch: Improve the search performance of
 module_kallsyms_on_each_symbol()

On Fri 2022-12-30 19:27:27, Zhen Lei wrote:
> Currently we traverse all symbols of all modules to find the specified
> function for the specified module. But in reality, we just need to find
> the given module and then traverse all the symbols in it.
> 
> Let's add a new parameter 'const char *modname' to function
> module_kallsyms_on_each_symbol(), then we can compare the module names
> directly in this function and call hook 'fn' after matching. If 'modname'
> is NULL, the symbols of all modules are still traversed for compatibility
> with other usage cases.
> 
> Phase1: mod1-->mod2..(subsequent modules do not need to be compared)
>                 |
> Phase2:          -->f1-->f2-->f3
> 
> Assuming that there are m modules, each module has n symbols on average,
> then the time complexity is reduced from O(m * n) to O(m) + O(n).
> 
> Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>

Looks good to me:

Reviewed-by: Petr Mladek <pmladek@...e.com>

Best Regards,
Petr