Re: [RFC PATCH 1/2] vmscan don't isolate too many pages

[Wu Fengguang <fengguang.wu@intel.com>]

On Tue, Jul 07, 2009 at 05:47:13PM +0800, KOSAKI Motohiro wrote:
> Subject: [PATCH] vmscan don't isolate too many pages
> 
> If the system have plenty threads or processes, concurrent reclaim can
> isolate very much pages.
> 
> And if other processes isolate _all_ pages on lru, the reclaimer can't find
> any reclaimable page and it makes accidental OOM.
> 
> The solusion is, we should restrict maximum number of isolated pages.
> (this patch use inactive_page/2)

Now I think this is a better solution than per-cpu throttling :)
Will test it tomorrow.

Acked-by: Wu Fengguang <fengguang.wu@intel.com>

> 
> FAQ
> -------
> Q: Why do you compared zone accumulate pages, not individual zone pages?
> A: If we check individual zone, #-of-reclaimer is restricted by smallest zone.
>    it mean decreasing the performance of the system having small dma zone.
> 
> 
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
> ---
>  mm/page_alloc.c |   27 +++++++++++++++++++++++++++
>  1 file changed, 27 insertions(+)
> 
> Index: b/mm/page_alloc.c
> ===================================================================
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1721,6 +1721,28 @@ gfp_to_alloc_flags(gfp_t gfp_mask)
>  	return alloc_flags;
>  }
>  
> +static bool too_many_isolated(struct zonelist *zonelist,
> +			      enum zone_type high_zoneidx, nodemask_t *nodemask)
> +{
> +	unsigned long nr_inactive = 0;
> +	unsigned long nr_isolated = 0;
> +	struct zoneref *z;
> +	struct zone *zone;
> +
> +	for_each_zone_zonelist_nodemask(zone, z, zonelist,
> +					high_zoneidx, nodemask) {
> +		if (!populated_zone(zone))
> +			continue;
> +
> +		nr_inactive += zone_page_state(zone, NR_INACTIVE_ANON);
> +		nr_inactive += zone_page_state(zone, NR_INACTIVE_FILE);
> +		nr_isolated += zone_page_state(zone, NR_ISOLATED_ANON);
> +		nr_isolated += zone_page_state(zone, NR_ISOLATED_FILE);
> +	}
> +
> +	return nr_isolated > nr_inactive;
> +}
> +
>  static inline struct page *
>  __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
>  	struct zonelist *zonelist, enum zone_type high_zoneidx,
> @@ -1789,6 +1811,11 @@ rebalance:
>  	if (p->flags & PF_MEMALLOC)
>  		goto nopage;
>  
> +	if (too_many_isolated(gfp_mask, zonelist, high_zoneidx, nodemask)) {
> +		schedule_timeout_uninterruptible(HZ/10);
> +		goto restart;
> +	}
> +
>  	/* Try direct reclaim and then allocating */
>  	page = __alloc_pages_direct_reclaim(gfp_mask, order,
>  					zonelist, high_zoneidx,
>