linux-kernel - Re: [RFC PATCH 5/5] refresh VM committed space after a task migration

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Message-Id: <1213119688.13882.13.camel@nimitz>
Date:	Tue, 10 Jun 2008 10:41:28 -0700
From:	Dave Hansen <dave@...ux.vnet.ibm.com>
To:	Andrea Righi <righi.andrea@...il.com>
Cc:	balbir@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
	kosaki.motohiro@...fujitsu.com, containers@...ts.osdl.org,
	menage@...gle.com, xemul@...nvz.org
Subject: Re: [RFC PATCH 5/5] refresh VM committed space after a task
	migration

On Tue, 2008-06-10 at 01:33 +0200, Andrea Righi wrote:
> +       preempt_disable();
> +       committed = atomic_long_read(&p->vm_committed_space);
> +       atomic_long_sub(committed, &old_mem->vmacct.vm_committed_space);
> +       atomic_long_add(committed, &mem->vmacct.vm_committed_space);
> +       preempt_enable();
>  out:
>         mmput(mm);
>  }

Why bother with the preempt stuff here?  What does the actually protect
against?  I assume that you're trying to keep other tasks that might run
on this CPU from seeing weird, inconsistent numbers in here.  Is there
some other looks that keeps *other* cpus from seeing this?

In any case, I think it needs a big, fat comment.

-- Dave

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