72  * Therefore KSM uses two data structures - the stable and the unstable tree.
74  * The stable tree holds pointers to all the merged pages (ksm pages), sorted
77  * and therefore this tree is called the stable tree.
79  * The stable tree node includes information required for reverse
83  * KSM maintains two types of nodes in the stable tree:
94  * In addition to the stable tree, KSM uses a second data structure called the
112  * 4) KSM never flushes the stable tree, which means that even if it were to
114  *    it is secured in the stable tree.  (When we scan a new page, we first
115  *    compare it against the stable tree, and then against the unstable tree.)
118  * stable trees and multiple unstable trees: one of each for each NUMA node.
148  * struct ksm_stable_node - node of the stable rbtree
149  * @node: rb node of this ksm page in the stable tree
157  * @nid: NUMA node id of stable tree in which linked (may not match kpfn)
161 		struct rb_node node;	/* when node of stable tree */
190  * @anon_vma: pointer to anon_vma for this mm,address, when in stable tree
196  * @head: pointer to stable_node heading this list in the stable tree
204 		struct anon_vma *anon_vma;	/* when stable */
216 		struct {		/* when listed from stable tree */
225 #define STABLE_FLAG	0x200	/* is listed from the stable tree */
227 /* The stable and unstable tree heads */
233 /* Recently migrated nodes of stable tree, pending proper placement */
257 /* The number of nodes in the stable tree */
278 /* Maximum number of page slots sharing a stable node */
672 	 * than we're counting as nodes in the stable tree; but ksm_do_scan  in break_ksm()
772  * stable and unstable pages from all nodes with roots in index 0. Otherwise,
773  * every node has its own stable and unstable tree.
795 		 * Put the stable node chain in the first dimension of  in alloc_stable_node_chain()
796 		 * the stable tree and at the same time remove the old  in alloc_stable_node_chain()
797 		 * stable node.  in alloc_stable_node_chain()
802 		 * Move the old stable node to the second dimension  in alloc_stable_node_chain()
870  * ksm_get_folio: checks if the page indicated by the stable node
874  * remove the stale node from the stable tree and return NULL.
875  * But beware, the stable node's page might be being migrated.
881  * "keyhole reference": access to the ksm page from the stable node peeps
883  * pointing back to this stable node.  This relies on freeing a PageAnon
965  * Removing rmap_item from stable or unstable tree.
966  * This function will clean the information from the stable/unstable tree.
1029  * Though it's very tempting to unmerge rmap_items from stable tree rather
1031  * that - an rmap_item is assigned to the stable tree after inserting ksm
1096 		 * The stable node did not yet appear stale to ksm_get_folio(),  in remove_stable_node()
1222 	/* Clean up stable nodes, but don't worry if some are still busy */  in unmerge_and_remove_all_rmap_items()
1462 	 * We need the folio lock to read a stable swapcache flag in  in try_to_merge_one_page()
1568 	/* Unstable nid is in union with stable anon_vma: remove first */  in try_to_merge_with_ksm_page()
1655 		 * stable nodes during lookup.  in stable_node_dup()
1711 			 * otherwise left as a stable pointer, the  in stable_node_dup()
1790  * stable_tree_search - search for page inside the stable tree
1792  * This function checks if there is a page inside the stable tree
1795  * This function returns the stable tree node of identical content if found,
1796  * -EBUSY if the stable node's page is being migrated, NULL otherwise.
1860 				 * this stable node to the chain.  in stable_tree_search()
1931 	 * from the case there was no chain in the stable  in stable_tree_search()
1979 	 * from the case there was no chain in the stable  in stable_tree_search()
2006  * stable_tree_insert - insert stable tree node pointing to new ksm page
2007  * into the stable tree.
2009  * This function returns the stable tree node just allocated on success,
2175  * rmap_items hanging off a given node of the stable tree, all sharing
2213  * cmp_and_merge_page - first see if page can be merged into the stable tree;
2216  * both transferred to the stable tree.
2269 	/* Start by searching for the folio in the stable tree */  in cmp_and_merge_page()
2286 			 * add its rmap_item to the stable tree.  in cmp_and_merge_page()
2320 			 * node in the stable tree and add both rmap_items.  in cmp_and_merge_page()
2333 			 * If we fail to insert the page into the stable tree,  in cmp_and_merge_page()
2335 			 * to a ksm page left outside the stable tree,  in cmp_and_merge_page()
3026 	 * to that page's node of the stable tree.  in rmap_walk_ksm()
3054 			/* Ignore the stable/unstable/sqnr flags */  in rmap_walk_ksm()
3247 		 * it is unsafe for them to touch the stable tree at this time.  in ksm_memory_callback()
3450 			 * Allocate stable and unstable together:  in merge_across_nodes_store()
3461 				/* Stable tree is empty but not the unstable */  in merge_across_nodes_store()