linux-kernel - Re: [PATCH] nextfd(2)

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Date:	Wed, 04 Apr 2012 11:08:22 -0700
From:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
To:	Ulrich Drepper <drepper@...il.com>
CC:	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Alexey Dobriyan <adobriyan@...il.com>,
	akpm@...ux-foundation.org, viro@...iv.linux.org.uk,
	torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] nextfd(2)

(4/4/12 10:49 AM), Ulrich Drepper wrote:
> On Wed, Apr 4, 2012 at 13:07, KOSAKI Motohiro<kosaki.motohiro@...il.com>  wrote:
>> Umm... I'm sorry. I haven't catch why OOM is related topic. Could you please
>> elaborate more?
>
> With fork you always have some copy-on-write (and worse for
> overcommit) just to then execute exec.  With a real spawn
> implementation you wouldn't have that.  A big problem if you, for
> instance, have to spawn a small helper from a gigantic process.

Ah, ok. I agree posix_spawn() has a chance to aim more momemory efficiency
than fork-exec. But in this purpose, vfork may be enough useful and be widely
accepted from userland folks.

Example, some daemon has a following patten,
  1. fork
  2. change /proc/<pid>/oom_adj
  3. exec

That's said, when adding linux specific knob, we need to add new posix_spawn flags
if we really need (or want) to replaces all userland. this seems very hard and doubtful
worth to me.

Ahh, note. I'm not against to implement posix_spawn() into the kernel. I only argue spawn()
can solve closefrom issue.
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