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From: Al Viro <viro@ZenIV.linux.org.uk>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Mimi Zohar <zohar@linux.vnet.ibm.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	". James Morris" <jmorris@namei.org>,
	linux-security-module@vger.kernel.org,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Oleg Nesterov <oleg@redhat.com>,
	David Miller <davem@davemloft.net>
Subject: Re: deferring __fput()
Date: Mon, 25 Jun 2012 13:14:36 +0100	[thread overview]
Message-ID: <20120625121436.GU14083@ZenIV.linux.org.uk> (raw)
In-Reply-To: <1340625805.2507.56.camel@laptop>

On Mon, Jun 25, 2012 at 02:03:25PM +0200, Peter Zijlstra wrote:
> On Sat, 2012-06-23 at 21:57 +0100, Al Viro wrote:
> > 3) at that point task_work is equal in size (and layout, BTW) to rcu_head.  So we can add it
> > into the same union in struct file where we already have list_head and rcu_head.  No space
> > eaten up.  fput() would, once the counter reaches 0, remove the file from list (the only
> > place walking that list skips the ones with zero refcount anyway) and, if we are in a normal
> > process, use task_work_add() to have __fput() done to it.  If we are in kernel thread or
> > atomic context, just move the sucker to global list and use schedule_work() to have said
> > list emptied and everything in it fed to __fput(). 
> 
> So we're now Ok with doing fput() async?
> 
> Last time I remember this coming up people thought this wasn't such a
> hot idea.

You mean, doing that from RCU callbacks?  Still a bad idea, IMO; you will end up with a context
switch and unpleasantness with delayed user-visible effects of syscalls.  With aio we did have
a delayed execution of fput() anyway; all that has changed there is that we use generic
mechanism instead of home-grown analog thereof.

I'll need to reread that thread to comment on the specifics (had been too long ago; I don't
remember the details), but...  See Linus' objections to full-async fput() circa this April
or March.  There's a reason why this patchset uses task_work_add() whenever possible.

  reply	other threads:[~2012-06-25 12:14 UTC|newest]

Thread overview: 54+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-06-22 12:44 deferring __fput() Mimi Zohar
2012-06-23  9:20 ` Al Viro
2012-06-23 19:45   ` Al Viro
2012-06-23 20:38     ` Oleg Nesterov
2012-06-23 21:01       ` Al Viro
2012-06-23 21:11         ` Al Viro
2012-06-24  4:16         ` Al Viro
2012-06-24 10:09           ` Al Viro
2012-06-24 16:54             ` Oleg Nesterov
2012-06-24 15:33           ` Oleg Nesterov
2012-06-25  6:03             ` Al Viro
2012-06-25 15:18               ` Oleg Nesterov
2012-06-27 18:37                 ` [PATCH 0/4] Was: " Oleg Nesterov
2012-06-27 18:37                   ` [PATCH 1/4] task_work: use the single-linked list to shrink sizeof(task_work) Oleg Nesterov
2012-06-27 18:37                   ` [PATCH 2/4] task_work: don't rely on PF_EXITING Oleg Nesterov
2012-06-27 18:38                   ` [PATCH 3/4] task_work: deal with task_work callbacks adding more work Oleg Nesterov
2012-06-27 18:38                   ` [PATCH 4/4] task_work: kill task_work->data Oleg Nesterov
2012-06-27 19:05                     ` Oleg Nesterov
2012-06-28  4:38                   ` [PATCH 0/4] Was: deferring __fput() Al Viro
2012-06-28 16:22                     ` Oleg Nesterov
2012-06-28 16:45                       ` Oleg Nesterov
2012-06-30  6:24                         ` Al Viro
2012-06-30 17:41                           ` Oleg Nesterov
2012-06-29  5:30                     ` Mimi Zohar
2012-06-29  8:33                       ` Al Viro
2012-06-29 13:02                         ` Mimi Zohar
2012-06-29 17:41                           ` Al Viro
2012-06-29 21:38                             ` Mimi Zohar
2012-06-29 23:56                               ` Mimi Zohar
2012-06-30  5:02                                 ` Al Viro
2012-07-01 19:50                                   ` Mimi Zohar
2012-07-01 20:57                                     ` Al Viro
2012-07-02  1:46                                       ` Mimi Zohar
2012-07-02  3:43                                         ` Al Viro
2012-07-02  5:11                                           ` Al Viro
2012-07-02 11:49                                             ` Mimi Zohar
2012-07-02 12:02                                               ` Al Viro
2012-07-02 13:01                                                 ` Mimi Zohar
2012-07-02 13:33                                                   ` Al Viro
2012-07-02 14:50                                                     ` Mimi Zohar
2012-08-21 13:05                                                       ` [PATCH] task_work: add a scheduling point in task_work_run() Eric Dumazet
2012-08-21 20:37                                                         ` Mimi Zohar
2012-08-21 21:32                                                           ` Eric Dumazet
2012-08-22  3:13                                                             ` Mimi Zohar
2012-08-22  5:27                                                         ` Michael Wang
2012-08-22  5:38                                                           ` Al Viro
2012-06-23 20:57     ` deferring __fput() Al Viro
2012-06-23 21:33       ` Al Viro
2012-06-24 15:20       ` Oleg Nesterov
2012-06-24 18:11         ` Oleg Nesterov
2012-06-25 12:03       ` Peter Zijlstra
2012-06-25 12:14         ` Al Viro [this message]
2012-06-25 13:19           ` Peter Zijlstra
2012-06-25 13:53             ` Al Viro

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