1 // SPDX-License-Identifier: GPL-2.0
34  * For two pages to be swapped in the shuffle, they must be free (on a
43 	 * Given we're dealing with randomly selected pfns in a zone we  in shuffle_valid_page()
55 	/* ...is the page free and currently on a free_area list? */  in shuffle_valid_page()
70  * Fisher-Yates shuffle the freelist which prescribes iterating through an
72  * the span, end_pfn - start_pfn.
75  * of bias in the distribution, like modulo bias or pseudo-random number
78  * be a perfect shuffle.
81 void __meminit __shuffle_zone(struct zone *z)  in __shuffle_zone()  argument
84 	unsigned long start_pfn = z->zone_start_pfn;  in __shuffle_zone()
85 	unsigned long end_pfn = zone_end_pfn(z);  in __shuffle_zone()
89 	spin_lock_irqsave(&z->lock, flags);  in __shuffle_zone()
97 		 * We expect page_i, in the sub-range of a zone being added  in __shuffle_zone()
102 		page_i = shuffle_valid_page(z, i, order);  in __shuffle_zone()
108 			 * Pick a random order aligned page in the zone span as  in __shuffle_zone()
109 			 * a swap target. If the selected pfn is a hole, retry  in __shuffle_zone()
110 			 * up to SHUFFLE_RETRY attempts find a random valid pfn  in __shuffle_zone()
113 			j = z->zone_start_pfn +  in __shuffle_zone()
114 				ALIGN_DOWN(get_random_long() % z->spanned_pages,  in __shuffle_zone()
116 			page_j = shuffle_valid_page(z, j, order);  in __shuffle_zone()
136 		list_swap(&page_i->lru, &page_j->lru);  in __shuffle_zone()
138 		pr_debug("%s: swap: %#lx -> %#lx\n", __func__, i, j);  in __shuffle_zone()
142 			spin_unlock_irqrestore(&z->lock, flags);  in __shuffle_zone()
144 			spin_lock_irqsave(&z->lock, flags);  in __shuffle_zone()
147 	spin_unlock_irqrestore(&z->lock, flags);  in __shuffle_zone()
151  * shuffle_free_memory - reduce the predictability of the page allocator
156 	struct zone *z;  in __shuffle_free_memory()  local
158 	for (z = pgdat->node_zones; z < pgdat->node_zones + MAX_NR_ZONES; z++)  in __shuffle_free_memory()
159 		shuffle_zone(z);  in __shuffle_free_memory()
179 	rand_bits--;  in shuffle_pick_tail()