From: email@example.com (Eric W. Biederman)
To: Anton Vorontsov <firstname.lastname@example.org>
Cc: "Oleg Nesterov" <email@example.com>,
"Arve Hjønnevåg" <firstname.lastname@example.org>,
"KOSAKI Motohiro" <email@example.com>,
"Greg Kroah-Hartman" <firstname.lastname@example.org>,
"San Mehat" <email@example.com>, "Colin Cross" <firstname.lastname@example.org>,
Subject: Re: [PATCH 1/3] procfs: Export next_tgid(), move it to kernel/pid.c
Date: Mon, 30 Jan 2012 17:51:20 -0800 [thread overview]
Message-ID: <email@example.com> (raw)
In-Reply-To: <20120130204920.GA27812@oksana.dev.rtsoft.ru> (Anton Vorontsov's message of "Tue, 31 Jan 2012 00:49:20 +0400")
Anton Vorontsov <firstname.lastname@example.org> writes:
> On Mon, Jan 30, 2012 at 02:43:12PM +0100, Oleg Nesterov wrote:
>> On 01/30, Anton Vorontsov wrote:
>> > We'd like to use this function in the android low memory killer driver, so
>> > let's export it.
>> I guess you mean 3/3.
>> If lowmem_shrink() can use next_tid() which is not really accurate,
>> then why tou can't simply change it to use rcu_read_lock ?
> Yes, in LMK driver we don't need to be accurate. I probably could use
> rcu_read_lock, but the plan was in not holding any global locks (in
> this case the rcu) at all, instead I'd like to hold just a reference
> of the task, which the driver is analyzing at this time. Once we decide
> (to kill or not to kill the task), we either send a signal (and drop
> the reference) or just drop the reference.
rcu_read_lock unless it is implemented wrong is free from a lock
perspective. rcu_read_lock only touches local state.
>From the look of your loop it already does a walk through the entire
process list so it looks to me like playing games with get_task_struct
and put_task_struct are going to be much more expensive.
proc grabs task references because we can't hold the rcu_read_lock
over a copy_to_user because that is a sleeping function.
You don't call anything that sleeps so rcu_read_lock should be
next prev parent reply other threads:[~2012-01-31 1:48 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-30 1:13 [PATCH 1/3] procfs: Export next_tgid(), move it to kernel/pid.c Anton Vorontsov
2012-01-30 2:22 ` Greg KH
2012-01-30 19:50 ` Anton Vorontsov
2012-01-30 3:26 ` Eric W. Biederman
2012-01-30 19:51 ` Anton Vorontsov
2012-01-30 13:43 ` Oleg Nesterov
2012-01-30 20:49 ` Anton Vorontsov
2012-01-31 1:51 ` Eric W. Biederman [this message]
2012-02-01 4:19 ` Anton Vorontsov
2012-02-01 4:37 ` Eric W. Biederman
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