linux-kernel - Re: [PATCH 3/3] Provide control over unmapped pages

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Date:	Wed, 1 Dec 2010 10:32:54 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Balbir Singh <balbir@...ux.vnet.ibm.com>
Cc:	linux-mm@...ck.org, Christoph Lameter <cl@...ux.com>,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	kvm <kvm@...r.kernel.org>
Subject: Re: [PATCH 3/3] Provide control over unmapped pages

On Tue, 30 Nov 2010 15:46:31 +0530
Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:

> Provide control using zone_reclaim() and a boot parameter. The
> code reuses functionality from zone_reclaim() to isolate unmapped
> pages and reclaim them as a priority, ahead of other mapped pages.
> 
> Signed-off-by: Balbir Singh <balbir@...ux.vnet.ibm.com>
> ---
>  include/linux/swap.h |    5 ++-
>  mm/page_alloc.c      |    7 +++--
>  mm/vmscan.c          |   72 +++++++++++++++++++++++++++++++++++++++++++++++++-
>  3 files changed, 79 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index eba53e7..78b0830 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -252,11 +252,12 @@ extern int vm_swappiness;
>  extern int remove_mapping(struct address_space *mapping, struct page *page);
>  extern long vm_total_pages;
>  
> -#ifdef CONFIG_NUMA
> -extern int zone_reclaim_mode;
>  extern int sysctl_min_unmapped_ratio;
>  extern int sysctl_min_slab_ratio;
>  extern int zone_reclaim(struct zone *, gfp_t, unsigned int);
> +extern bool should_balance_unmapped_pages(struct zone *zone);
> +#ifdef CONFIG_NUMA
> +extern int zone_reclaim_mode;
>  #else
>  #define zone_reclaim_mode 0
>  static inline int zone_reclaim(struct zone *z, gfp_t mask, unsigned int order)
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 62b7280..4228da3 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1662,6 +1662,9 @@ zonelist_scan:
>  			unsigned long mark;
>  			int ret;
>  
> +			if (should_balance_unmapped_pages(zone))
> +				wakeup_kswapd(zone, order);
> +

Hm, I'm not sure the final vision of this feature. Does this reclaiming feature
can't be called directly via balloon driver just before alloc_page() ?

Do you need to keep page caches small even when there are free memory on host ?

Thanks,
-Kame

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