linux-kernel - Re: [PATCH -tip 3/3] kprobes: cleanup: use list instead of hlist for insn

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Date:	Tue, 30 Jun 2009 17:47:48 -0400
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	lkml <linux-kernel@...r.kernel.org>,
	systemtap <systemtap@...rces.redhat.com>,
	DLE <dle-develop@...ts.sourceforge.net>,
	Jim Keniston <jkenisto@...ibm.com>
Subject: Re: [PATCH -tip 3/3] kprobes: cleanup: use list instead of hlist
 for insn_pages

Ingo Molnar wrote:
> * Masami Hiramatsu <mhiramat@...hat.com> wrote:
> 
>> Use struct list instead of struct hlist for managing insn_pages, 
>> because insn_pages doesn't use hash table.
> 
>>  struct kprobe_insn_page {
>> -	struct hlist_node hlist;
>> +	struct list_head list;
> 
> Hm, you know that this increases the size of kprobe_insn_page by 4/8 
> bytes, right?

Sure, that will increase size.

> hlists are not just used for hashes - but also when we want a more 
> compact / smaller list head.

Oh, I thought hlists are used for hash tables...

> 
> How many kprobe_insn_page's can be allocated in the system, 
> maximally?

It's depends on how many probes you will use, but logically,
1 kprobe_insn_pages is allocated per 4096/16 = 256 probes.
So, if you use 25,600 probes on your system, memory
consumption will increase 400/800 bytes.

Thank you,

-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America), Inc.
Software Solutions Division

e-mail: mhiramat@...hat.com

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