linux-kernel - Re: [PATCH] ptrace: cleanup ptrace_init_task()->ptrace

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Date:	Fri, 30 Oct 2009 18:56:20 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Roland McGrath <roland@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ptrace: cleanup ptrace_init_task()->ptrace_link() path

On Sat, 31 Oct 2009 01:55:07 +0100 Oleg Nesterov <oleg@...hat.com> wrote:

> On 10/30, Andrew Morton wrote:
> >
> > On Fri, 30 Oct 2009 00:56:56 +0100
> > Oleg Nesterov <oleg@...hat.com> wrote:
> >
> > >  ptrace
> >
> > Speaking of which, I'm still sitting on
> > do_wait-optimization-do-not-place-sub-threads-on-task_struct-children-list.patch.
> 
> (this patch has nothing to do with ptrace)
> 
> > Should I drop it?
> 
> Why? I think this is good optimization and imho cleanup.
> 
> There is no point to have sub-thread in ->children list and this
> slows down do_wait() if a child has a lot of threads, it has to
> iterate over all sub-threads just to filter them out.
> 

On 17 Sep you said:

: Yes, risky... God knows who can do list_for_each(->children) and expect to
: find the sub-threads. But this is obviously good optimization/simplification.
:
: It is just ugly to place sub-threads on ->children list, this buys nothing
: but slown downs do_wait(). (this was needed, afaics, to handle ptraced but
: not re-parented threads a long ago).

so that's why I didn't merge it into 2.6.32.  Is the patch still
considered "risky"?

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