linux-kernel - Re: [PATCH v7 00/11] kallsyms: Optimizes the performance of lookup symbols

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Date:   Wed, 26 Oct 2022 12:03:36 -0700
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
Cc:     Josh Poimboeuf <jpoimboe@...nel.org>,
        Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Petr Mladek <pmladek@...e.com>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
        Masahiro Yamada <masahiroy@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-modules@...r.kernel.org,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH v7 00/11] kallsyms: Optimizes the performance of lookup
 symbols

On Wed, Oct 26, 2022 at 02:44:36PM +0800, Leizhen (ThunderTown) wrote:
> On 2022/10/26 1:53, Luis Chamberlain wrote:
> > This answers how we don't use a hash table, the question was *should* we
> > use one?
> 
> I'm not the original author, and I can only answer now based on my understanding. Maybe
> the original author didn't think of the hash method, or he has weighed it out.
> 
> Hash is a good solution if only performance is required and memory overhead is not
> considered. Using hash will increase the memory size by up to "4 * kallsyms_num_syms +
> 4 * ARRAY_SIZE(hashtable)" bytes, kallsyms_num_syms is about 1-2 million.
> 
> Because I don't know what hash algorithm will be used, the cost of generating the
> hash value corresponding to the symbol name is unknown now. But I think it's gonna
> be small. But it definitely needs a simpler algorithm, the tool needs to implement
> the same hash algorithm.

For instance, you can look at evaluating if alloc_large_system_hash() would help.

  Luis