Re: [patch] mm: clear node in N_HIGH_MEMORY and stop kswapd when all memory is offlined

[Lee Schermerhorn <Lee.Schermerhorn@hp.com>]

On Wed, 2009-10-07 at 01:24 -0700, David Rientjes wrote:
> On Mon, 5 Oct 2009, Lee Schermerhorn wrote:
> 
> > [PATCH 11/11] hugetlb:  offload [un]registration of sysfs attr to worker thread
> > 
> > Against:  2.6.31-mmotm-090925-1435
> > 
> > New in V6
> > 
> > V7:  + remove redundant check for memory{ful|less} node from 
> >        node_hugetlb_work().  Rely on [added] return from
> >        hugetlb_register_node() to differentiate between transitions
> >        to/from memoryless state.
> > 
> 
> That doesn't work because the memory hotplug code doesn't clear the 
> N_HIGH_MEMORY bit for status_change_nid on MEM_OFFLINE, so 
> hugetlb_register_node() will always return true under such conditions.
> 
> The following should fix it.  Christoph?
> 
> 

Almost missed this one because of the subject.  

What shall we do with this for the huge pages controls series?  

Options:

1) leave series as is, and note that it depends on this patch?

2) Include this patch [or the subset that clears the N_HIGH_MEMORY node
state--maybe leave the kswapd handling separate?] in the series?


Lee

> 
> mm: clear node in N_HIGH_MEMORY and stop kswapd when all memory is offlined
> 
> When memory is hot-removed, its node must be cleared in N_HIGH_MEMORY if
> there are no present pages left.
> 
> In such a situation, kswapd must also be stopped since it has nothing
> left to do.
> 
> Cc: Christoph Lameter <cl@linux-foundation.org>
> Cc: Yasunori Goto <y-goto@jp.fujitsu.com>
> Cc: Mel Gorman <mel@csn.ul.ie>
> Signed-off-by: David Rientjes <rientjes@google.com>
> ---
>  include/linux/swap.h |    1 +
>  mm/memory_hotplug.c  |    4 ++++
>  mm/vmscan.c          |   28 ++++++++++++++++++++++------
>  3 files changed, 27 insertions(+), 6 deletions(-)
> 
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -273,6 +273,7 @@ extern int scan_unevictable_register_node(struct node *node);
>  extern void scan_unevictable_unregister_node(struct node *node);
>  
>  extern int kswapd_run(int nid);
> +extern void kswapd_stop(int nid);
>  
>  #ifdef CONFIG_MMU
>  /* linux/mm/shmem.c */
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -838,6 +838,10 @@ repeat:
>  
>  	setup_per_zone_wmarks();
>  	calculate_zone_inactive_ratio(zone);
> +	if (!node_present_pages(node)) {
> +		node_clear_state(node, N_HIGH_MEMORY);
> +		kswapd_stop(node);
> +	}
>  
>  	vm_total_pages = nr_free_pagecache_pages();
>  	writeback_set_ratelimit();
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2163,6 +2163,7 @@ static int kswapd(void *p)
>  	order = 0;
>  	for ( ; ; ) {
>  		unsigned long new_order;
> +		int ret;
>  
>  		prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
>  		new_order = pgdat->kswapd_max_order;
> @@ -2174,19 +2175,23 @@ static int kswapd(void *p)
>  			 */
>  			order = new_order;
>  		} else {
> -			if (!freezing(current))
> +			if (!freezing(current) && !kthread_should_stop())
>  				schedule();
>  
>  			order = pgdat->kswapd_max_order;
>  		}
>  		finish_wait(&pgdat->kswapd_wait, &wait);
>  
> -		if (!try_to_freeze()) {
> -			/* We can speed up thawing tasks if we don't call
> -			 * balance_pgdat after returning from the refrigerator
> -			 */
> +		ret = try_to_freeze();
> +		if (kthread_should_stop())
> +			break;
> +
> +		/*
> +		 * We can speed up thawing tasks if we don't call balance_pgdat
> +		 * after returning from the refrigerator
> +		 */
> +		if (!ret)
>  			balance_pgdat(pgdat, order);
> -		}
>  	}
>  	return 0;
>  }
> @@ -2441,6 +2446,17 @@ int kswapd_run(int nid)
>  	return ret;
>  }
>  
> +/*
> + * Called by memory hotplug when all memory in a node is offlined.
> + */
> +void kswapd_stop(int nid)
> +{
> +	struct task_struct *kswapd = NODE_DATA(nid)->kswapd;
> +
> +	if (kswapd)
> +		kthread_stop(kswapd);
> +}
> +
>  static int __init kswapd_init(void)
>  {
>  	int nid;

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