linux-kernel - Re: [PATCH] perf-event/cgroup: explicitly init the early

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Message-ID: <CAHz2CGW0D6GpbP7Tps2KoN8av_OUEzO9xGvpV_XwoHgFQ36sOw@mail.gmail.com>
Date:	Tue, 22 Apr 2014 15:12:45 +0800
From:	Jianyu Zhan <nasa4836@...il.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	a.p.zijlstra@...llo.nl, paulus@...ba.org, mingo@...hat.com,
	acme@...nel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] perf-event/cgroup: explicitly init the early_init field

On Tue, Apr 22, 2014 at 2:06 PM, Ingo Molnar <mingo@...nel.org> wrote:
> How can that field ever be nonzero?
>
> I.e. under what exact circumstances does this patch make sense?

Hi, Ingo,

More explanation.

Sure, for this global variable struct, if not initailized, its all
fields will be initialized
to 0 or null(depending on its type).  The point here is no to deprive
the rights of compiler/linker of doing this initialization, it is mainly for
documentation reason. Actually this field's value would affect how ->css_alloc
should implemented.

Concretely, if early_init is nonzero, then ->css_alloc *must not* call kzalloc,
because in cgroup implementation, ->css_alloc will be called earlier before
mm_init().

I don't think that the value of one field(early_init) has a so subtle
restrition on the another field(css_alloc) is a good thing, but since
it is there,
docment it should be needed.

I could resend the patch with  more comment.

Thanks,
Jianyu Zhan
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