linux-kernel - Re: [PATCH][RESEND] nommu: yield CPU periodically while disposing large VM

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Message-Id: <20101112101645.DFF9.A69D9226@jp.fujitsu.com>
Date:	Sun, 14 Nov 2010 14:07:08 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	"Steven J. Magnani" <steve@...idescorp.com>
Cc:	kosaki.motohiro@...fujitsu.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH][RESEND] nommu: yield CPU periodically while disposing large VM

> Depending on processor speed, page size, and the amount of memory a process
> is allowed to amass, cleanup of a large VM may freeze the system for many
> seconds. This can result in a watchdog timeout.
> 
> Make sure other tasks receive some service when cleaning up large VMs.
> 
> Signed-off-by: Steven J. Magnani <steve@...idescorp.com>
> ---
> diff -uprN a/mm/nommu.c b/mm/nommu.c
> --- a/mm/nommu.c	2010-10-21 07:42:23.000000000 -0500
> +++ b/mm/nommu.c	2010-10-21 07:46:50.000000000 -0500
> @@ -1656,6 +1656,7 @@ SYSCALL_DEFINE2(munmap, unsigned long, a
>  void exit_mmap(struct mm_struct *mm)
>  {
>  	struct vm_area_struct *vma;
> +	unsigned long next_yield = jiffies + HZ;
>  
>  	if (!mm)
>  		return;
> @@ -1668,6 +1669,11 @@ void exit_mmap(struct mm_struct *mm)
>  		mm->mmap = vma->vm_next;
>  		delete_vma_from_mm(vma);
>  		delete_vma(mm, vma);
> +		/* Yield periodically to prevent watchdog timeout */
> +		if (time_after(jiffies, next_yield)) {
> +			cond_resched();
> +			next_yield = jiffies + HZ;
> +		}

If watchdog tiemr interval is less than HZ, this logic doesn't work. right?
If so, I would suggest just remove time_after() and call cond_resched() every time
because cond_resched is no-op if TIF_NEED_RESCHED is not setted.



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