linux-kernel - Re: deferring _

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Message-ID: <20120623203800.GA10306@redhat.com>
Date:	Sat, 23 Jun 2012 22:38:00 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Mimi Zohar <zohar@...ux.vnet.ibm.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	". James Morris" <jmorris@...ei.org>,
	linux-security-module@...r.kernel.org,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: deferring __fput()

On 06/23, Al Viro wrote:
>
> BTW, I really wonder why do we need to have that void *data in task_work; we can
> always embed the sucker into a bigger struct (if nothing else, task_work +
> void *data) and get to it via container_of().  And in quite a few cases we don't
> want that data thing at all.

Yes, it is not strictly needed. From the changelog:

	"struct task_work" can be embedded in another struct, still it has "void
	*data" to handle the most common/simple case.

Namely, for keyctl_session_to_parent(). Probably it has ->data just because
I failed to invent the good name for the struct with task_work + cred.

> Moreover, the reasons to use hlist_head instead of
> a single forward pointer are very thin on the ground:

Oh, yes, there is no any reason. Except the code looks a bit simpler.

> Oleg, do you see any reasons why trimming it down to forward pointer + callback
> pointer wouldn't work?

OK. will do.

> Matter of fact, it would become identical to struct rcu_head
> after that...

This is not clear to me... Why this is good?

I understand that sizeof(task_work) == sizeof(rcu_head) would be
nice, probably you meant just this?

Oleg.

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