linux-kernel - Re: [PATCH v2] jump_label: reduce the size of struct static

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Date:   Sat, 21 Jan 2017 08:07:01 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Jason Baron <jbaron@...mai.com>
Cc:     peterz@...radead.org, rostedt@...dmis.org,
        linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v2] jump_label: reduce the size of struct static_key


* Jason Baron <jbaron@...mai.com> wrote:

> >For example the last line could sure be written as:
> >
> >			key->entries = jlm->entries;
> >			key->type |= static_key_type(key);
> >
> >right?
> 
> Hi,
> 
> So that is going to over-write the static_key_type(key) in the first
> assignment. If the order is reversed we can't just |= in the pointer type.

Indeed, I missed that.

> How about:
> 
> static void jump_key_set_entries(struct static_key *key, struct jump_entry *entries)
> {
>        unsigned long type;
> 
>        type = static_key_type(key);
>        key->entries = entries;
>        key->type |= type;
> }
> 
> and then we can also add:
> 
> void jump_key_set_mod(struct static_key *key, struct static_key_mod *mod)
> 
> doing basically the same thing. That will avoid the casts that you called
> out.
> 
> better?

Yeah - and it should generate the exact same code, right?

I'd also add a short comment to the helper function that points out the 
union/aliasing, in case anyone is wondering.

Thanks,

	Ingo