Re: [PATCH v8 4/9] kallsyms: Reduce the memory occupied by kallsyms_seqs_of_names[]

From: "Leizhen (ThunderTown)" <thunder.leizhen@huawei.com>
To: David Laight <David.Laight@ACULAB.COM>,
	Josh Poimboeuf <jpoimboe@kernel.org>,
	Jiri Kosina <jikos@kernel.org>, Miroslav Benes <mbenes@suse.cz>,
	Petr Mladek <pmladek@suse.com>,
	Joe Lawrence <joe.lawrence@redhat.com>,
	"live-patching@vger.kernel.org" <live-patching@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Masahiro Yamada <masahiroy@kernel.org>,
	Alexei Starovoitov <ast@kernel.org>, Jiri Olsa <jolsa@kernel.org>,
	Kees Cook <keescook@chromium.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	"Luis Chamberlain" <mcgrof@kernel.org>,
	"linux-modules@vger.kernel.org" <linux-modules@vger.kernel.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	"Ingo Molnar" <mingo@redhat.com>
Subject: Re: [PATCH v8 4/9] kallsyms: Reduce the memory occupied by kallsyms_seqs_of_names[]
Date: Mon, 7 Nov 2022 16:01:27 +0800	[thread overview]
Message-ID: <59edf022-45a7-3cee-a7e7-4b6480e9b679@huawei.com> (raw)
In-Reply-To: <bd30cbc9b7594261a7b9da26e9c98da4@AcuMS.aculab.com>

On 2022/11/2 20:00, David Laight wrote:
> From: Zhen Lei
>> Sent: 02 November 2022 08:49
>>
>> kallsyms_seqs_of_names[] records the symbol index sorted by address, the
>> maximum value in kallsyms_seqs_of_names[] is the number of symbols. And
>> 2^24 = 16777216, which means that three bytes are enough to store the
>> index. This can help us save (1 * kallsyms_num_syms) bytes of memory.
> 
> You can get the compiler to do the 'heavy lifting' for you.
> 
> struct uint24 {
>     unsigned int val24:24;
> } __attribute__((packed));

This method depends on byte order. If the byte order of the tool is
different from that of the kernel, it's a problem. For example,
cross-compile PowerPC kernel on x86.

> 
> struct uint24 table[1024];
> 
> works fine.
> 
> 	David
> 
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)
> 
> 
> .
> 

-- 
Regards,
  Zhen Lei