内存域水印值：min_free

1、内存域水印值：需要为关键性分配保留的内存空间的最小值；该值保存在全局变量min_free_kbytes中

2、内存域水印值的计算由函数init_per_zone_pages_min完成：

/*

 * Initialise min_free_kbytes.

 *

 * For small machines we want it small (128k min).  For large machines

 * we want it large (64MB max).  But it is not linear, because network

 * bandwidth does not increase linearly with machine size.  We use

 *

 * 	min_free_kbytes = 4 * sqrt(lowmem_kbytes), for better accuracy:

 *	min_free_kbytes = sqrt(lowmem_kbytes * 16)

 *

 * which yields

 *

 * 16MB:	512k

 * 32MB:	724k

 * 64MB:	1024k

 * 128MB:	1448k

 * 256MB:	2048k

 * 512MB:	2896k

 * 1024MB:	4096k

 * 2048MB:	5792k

 * 4096MB:	8192k

 * 8192MB:	11584k

 * 16384MB:	16384k

 */

static int __init init_per_zone_pages_min(void)

{

	unsigned long lowmem_kbytes;

	lowmem_kbytes = nr_free_buffer_pages() * (PAGE_SIZE >> 10);

	min_free_kbytes = int_sqrt(lowmem_kbytes * 16);

	if (min_free_kbytes < 128)

		min_free_kbytes = 128;

	if (min_free_kbytes > 65536)

		min_free_kbytes = 65536;

	setup_per_zone_pages_min();

	setup_per_zone_lowmem_reserve();

	return 0;

}

3、setup_per_zone_pages_min设置struct zone的pages_min、pages_low、pages_high成员

/**

 * setup_per_zone_pages_min - called when min_free_kbytes changes.

 *

 * Ensures that the pages_{min,low,high} values for each zone are set correctly

 * with respect to min_free_kbytes.

 */

void setup_per_zone_pages_min(void)

{

	unsigned long pages_min = min_free_kbytes >> (PAGE_SHIFT - 10);

	unsigned long lowmem_pages = 0;

	struct zone *zone;

	unsigned long flags;

	/* Calculate total number of !ZONE_HIGHMEM pages */

	for_each_zone(zone) {

		if (!is_highmem(zone))

			lowmem_pages += zone->present_pages;

	}

	for_each_zone(zone) {

		u64 tmp;

		spin_lock_irqsave(&zone->lru_lock, flags);

		tmp = (u64)pages_min * zone->present_pages;

		do_div(tmp, lowmem_pages);

		if (is_highmem(zone)) {

			/*

			 * __GFP_HIGH and PF_MEMALLOC allocations usually don't

			 * need highmem pages, so cap pages_min to a small

			 * value here.

			 *

			 * The (pages_high-pages_low) and (pages_low-pages_min)

			 * deltas controls asynch page reclaim, and so should

			 * not be capped for highmem.

			 */

			int min_pages;

			min_pages = zone->present_pages / 1024;

			if (min_pages < SWAP_CLUSTER_MAX)

				min_pages = SWAP_CLUSTER_MAX;

			if (min_pages > 128)

				min_pages = 128;

			zone->pages_min = min_pages;

		} else {

			/*

			 * If it's a lowmem zone, reserve a number of pages

			 * proportionate to the zone's size.

			 */

			zone->pages_min = tmp;

		}

		zone->pages_low   = zone->pages_min + (tmp >> 2);

		zone->pages_high  = zone->pages_min + (tmp >> 1);

		setup_zone_migrate_reserve(zone);

		spin_unlock_irqrestore(&zone->lru_lock, flags);

	}

	/* update totalreserve_pages */

	calculate_totalreserve_pages();

}

4、setup_per_zone_lowmem_reserve主要用作设置lowmem_reserve值

/*

 * setup_per_zone_lowmem_reserve - called whenever

 *	sysctl_lower_zone_reserve_ratio changes.  Ensures that each zone

 *	has a correct pages reserved value, so an adequate number of

 *	pages are left in the zone after a successful __alloc_pages().

 */

static void setup_per_zone_lowmem_reserve(void)

{

	struct pglist_data *pgdat;

	enum zone_type j, idx;

	for_each_online_pgdat(pgdat) {

		for (j = 0; j < MAX_NR_ZONES; j++) {

			struct zone *zone = pgdat->node_zones + j;

			unsigned long present_pages = zone->present_pages;

			zone->lowmem_reserve[j] = 0;

			idx = j;

			while (idx) {

				struct zone *lower_zone;

				idx--;

				if (sysctl_lowmem_reserve_ratio[idx] < 1)

					sysctl_lowmem_reserve_ratio[idx] = 1;

				lower_zone = pgdat->node_zones + idx;

				lower_zone->lowmem_reserve[j] = present_pages /

					sysctl_lowmem_reserve_ratio[idx];

				present_pages += lower_zone->present_pages;

			}

		}

	}

	/* update totalreserve_pages */

	calculate_totalreserve_pages();

}

除数的默认值，对低端内存是256，对高端内存是32

/*

 * results with 256, 32 in the lowmem_reserve sysctl:

 *	1G machine -> (16M dma, 800M-16M normal, 1G-800M high)

 *	1G machine -> (16M dma, 784M normal, 224M high)

 *	NORMAL allocation will leave 784M/256 of ram reserved in the ZONE_DMA

 *	HIGHMEM allocation will leave 224M/32 of ram reserved in ZONE_NORMAL

 *	HIGHMEM allocation will (224M+784M)/256 of ram reserved in ZONE_DMA

 *

 * TBD: should special case ZONE_DMA32 machines here - in those we normally

 * don't need any ZONE_NORMAL reservation

 */

int sysctl_lowmem_reserve_ratio[MAX_NR_ZONES-1] = {

#ifdef CONFIG_ZONE_DMA

	 256,

#endif

#ifdef CONFIG_ZONE_DMA32

	 256,

#endif

#ifdef CONFIG_HIGHMEM

	 32,

#endif

	 32,

};

巴特西

内存域水印值：min_free_kbytes

最新文章

热门文章