linux-kernel - Re: [PATCH] ns: move free_nsproxy() out of do

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Message-Id: <20120713140806.b3d0fda8.akpm@linux-foundation.org>
Date:	Fri, 13 Jul 2012 14:08:06 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:	Serge Hallyn <serge.hallyn@...onical.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	"Dmitry V. Levin" <ldv@...linux.org>,
	Pavel Emelyanov <xemul@...nvz.org>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Doug Ledford <dledford@...hat.com>,
	linux-kernel@...r.kernel.org, containers@...ts.linux-foundation.org
Subject: Re: [PATCH] ns: move free_nsproxy() out of do_exit() path

On Fri, 13 Jul 2012 14:48:08 +0300
"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com> wrote:

> From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
> 
> free_nsproxy() is too heavy to be on exit path. Let's free namespaces
> asynchronously to not block exit_group() syscall.

Please be specific, and complete.

Why is it "too heavy"?  Where is the time being spent?  Is it spent in
D state or is it spent burning CPU cycles?  Does the patch simply
offload the work into kernel threads, providing no net gain?

> The patch also fixes bug with free namespace without synchronize_rcu() through
> put_nsproxy().

I just don't understand this description.  Please send a new one which
includes all details about the bug, including a description of
the user-visible effects of the bug.

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