linux-kernel - Re: [PATCH 2/3] fork: reset mm->pinned

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Message-Id: <20140619135820.57c4934dd613c5e723f9ca82@linux-foundation.org>
Date:	Thu, 19 Jun 2014 13:58:20 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Vladimir Davydov <vdavydov@...allels.com>
Cc:	<oleg@...hat.com>, <rientjes@...gle.com>, <cl@...ux.com>,
	<linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] fork: reset mm->pinned_vm

On Thu, 19 Jun 2014 13:07:47 +0400 Vladimir Davydov <vdavydov@...allels.com> wrote:

> mm->pinned_vm counts pages of mm's address space that were permanently
> pinned in memory by increasing their reference counter. The counter was
> introduced by commit bc3e53f682d9 ("mm: distinguish between mlocked and
> pinned pages"), while before it locked_vm had been used for such pages.
> 
> Obviously, we should reset the counter on fork if !CLONE_VM, just like
> we do with locked_vm, but currently we don't. Let's fix it.
> 
> ...
>
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -534,6 +534,7 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p)
>  	atomic_long_set(&mm->nr_ptes, 0);
>  	mm->map_count = 0;
>  	mm->locked_vm = 0;
> +	mm->pinned_vm = 0;
>  	memset(&mm->rss_stat, 0, sizeof(mm->rss_stat));
>  	spin_lock_init(&mm->page_table_lock);
>  	mm_init_cpumask(mm);

What are the runtime effects of this?  I think it is only
"/proc/pid/status:VmPin is screwed up", because we don't use vm_pinned
in rlimit checks.  Yes?

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