linux-kernel - Re: [RFC PATCH 10/12] mm: add the buddy system interface

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Date:	Tue, 09 Jun 2015 16:12:32 +0900
From:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Xishi Qiu <qiuxishi@...wei.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	nao.horiguchi@...il.com, Yinghai Lu <yinghai@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>, mingo@...e.hu,
	Xiexiuqi <xiexiuqi@...wei.com>,
	Hanjun Guo <guohanjun@...wei.com>,
	"Luck, Tony" <tony.luck@...el.com>
CC:	Linux MM <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 10/12] mm: add the buddy system interface

On 2015/06/04 22:04, Xishi Qiu wrote:
> Add the buddy system interface for address range mirroring feature.
> Allocate mirrored pages in MIGRATE_MIRROR list. If there is no mirrored pages
> left, use other types pages.
>
> Signed-off-by: Xishi Qiu <qiuxishi@...wei.com>
> ---
>   mm/page_alloc.c | 40 +++++++++++++++++++++++++++++++++++++++-
>   1 file changed, 39 insertions(+), 1 deletion(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index d4d2066..0fb55288 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -599,6 +599,26 @@ static inline bool is_mirror_pfn(unsigned long pfn)
>
>   	return false;
>   }
> +
> +static inline bool change_to_mirror(gfp_t gfp_flags, int high_zoneidx)
> +{
> +	/*
> +	 * Do not alloc mirrored memory below 4G, because 0-4G is
> +	 * all mirrored by default, and the list is always empty.
> +	 */
> +	if (high_zoneidx < ZONE_NORMAL)
> +		return false;
> +
> +	/* Alloc mirrored memory for only kernel */
> +	if (gfp_flags & __GFP_MIRROR)
> +		return true;

GFP_KERNEL itself should imply mirror, I think.

> +
> +	/* Alloc mirrored memory for both user and kernel */
> +	if (sysctl_mirrorable)
> +		return true;

Reading this, I think this sysctl is not good. The user cannot know what is mirrored
because memory may not be mirrored until the sysctl is set.

Thanks,
-Kame


> +
> +	return false;
> +}
>   #endif
>
>   /*
> @@ -1796,7 +1816,10 @@ struct page *buffered_rmqueue(struct zone *preferred_zone,
>   			WARN_ON_ONCE(order > 1);
>   		}
>   		spin_lock_irqsave(&zone->lock, flags);
> -		page = __rmqueue(zone, order, migratetype);
> +		if (is_migrate_mirror(migratetype))
> +			page = __rmqueue_smallest(zone, order, migratetype);
> +		else
> +			page = __rmqueue(zone, order, migratetype);
>   		spin_unlock(&zone->lock);
>   		if (!page)
>   			goto failed;
> @@ -2928,6 +2951,11 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order,
>   	if (IS_ENABLED(CONFIG_CMA) && ac.migratetype == MIGRATE_MOVABLE)
>   		alloc_flags |= ALLOC_CMA;
>
> +#ifdef CONFIG_MEMORY_MIRROR
> +	if (change_to_mirror(gfp_mask, ac.high_zoneidx))
> +		ac.migratetype = MIGRATE_MIRROR;
> +#endif
> +
>   retry_cpuset:
>   	cpuset_mems_cookie = read_mems_allowed_begin();
>
> @@ -2943,9 +2971,19 @@ retry_cpuset:
>
>   	/* First allocation attempt */
>   	alloc_mask = gfp_mask|__GFP_HARDWALL;
> +retry:
>   	page = get_page_from_freelist(alloc_mask, order, alloc_flags, &ac);
>   	if (unlikely(!page)) {
>   		/*
> +		 * If there is no mirrored memory, we will alloc other
> +		 * types memory.
> +		 */
> +		if (is_migrate_mirror(ac.migratetype)) {
> +			ac.migratetype = gfpflags_to_migratetype(gfp_mask);
> +			goto retry;
> +		}
> +
> +		/*
>   		 * Runtime PM, block IO and its error handling path
>   		 * can deadlock because I/O on the device might not
>   		 * complete.
>


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