From ef53d16cded7f89b3843b7a96970dab897843ea5 Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Fri, 22 Feb 2013 16:36:12 -0800 Subject: ksm: allocate roots when needed It is a pity to have MAX_NUMNODES+MAX_NUMNODES tree roots statically allocated, particularly when very few users will ever actually tune merge_across_nodes 0 to use more than 1+1 of those trees. Not a big deal (only 16kB wasted on each machine with CONFIG_MAXSMP), but a pity. Start off with 1+1 statically allocated, then if merge_across_nodes is ever tuned, allocate for nr_node_ids+nr_node_ids. Do not attempt to free up the extra if it's tuned back, that would be a waste of effort. Signed-off-by: Hugh Dickins Cc: Mel Gorman Cc: Petr Holasek Cc: Andrea Arcangeli Cc: Izik Eidus Cc: Johannes Weiner Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds diff --git a/mm/ksm.c b/mm/ksm.c index d61cba6..ab2ba9a 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -183,8 +183,10 @@ struct rmap_item { #define STABLE_FLAG 0x200 /* is listed from the stable tree */ /* The stable and unstable tree heads */ -static struct rb_root root_unstable_tree[MAX_NUMNODES]; -static struct rb_root root_stable_tree[MAX_NUMNODES]; +static struct rb_root one_stable_tree[1] = { RB_ROOT }; +static struct rb_root one_unstable_tree[1] = { RB_ROOT }; +static struct rb_root *root_stable_tree = one_stable_tree; +static struct rb_root *root_unstable_tree = one_unstable_tree; /* Recently migrated nodes of stable tree, pending proper placement */ static LIST_HEAD(migrate_nodes); @@ -224,8 +226,10 @@ static unsigned int ksm_thread_sleep_millisecs = 20; #ifdef CONFIG_NUMA /* Zeroed when merging across nodes is not allowed */ static unsigned int ksm_merge_across_nodes = 1; +static int ksm_nr_node_ids = 1; #else #define ksm_merge_across_nodes 1U +#define ksm_nr_node_ids 1 #endif #define KSM_RUN_STOP 0 @@ -508,7 +512,7 @@ static void remove_node_from_stable_tree(struct stable_node *stable_node) list_del(&stable_node->list); else rb_erase(&stable_node->node, - &root_stable_tree[NUMA(stable_node->nid)]); + root_stable_tree + NUMA(stable_node->nid)); free_stable_node(stable_node); } @@ -644,7 +648,7 @@ static void remove_rmap_item_from_tree(struct rmap_item *rmap_item) BUG_ON(age > 1); if (!age) rb_erase(&rmap_item->node, - &root_unstable_tree[NUMA(rmap_item->nid)]); + root_unstable_tree + NUMA(rmap_item->nid)); ksm_pages_unshared--; rmap_item->address &= PAGE_MASK; } @@ -742,7 +746,7 @@ static int remove_all_stable_nodes(void) int nid; int err = 0; - for (nid = 0; nid < nr_node_ids; nid++) { + for (nid = 0; nid < ksm_nr_node_ids; nid++) { while (root_stable_tree[nid].rb_node) { stable_node = rb_entry(root_stable_tree[nid].rb_node, struct stable_node, node); @@ -1150,6 +1154,7 @@ static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item, static struct page *stable_tree_search(struct page *page) { int nid; + struct rb_root *root; struct rb_node **new; struct rb_node *parent; struct stable_node *stable_node; @@ -1163,8 +1168,9 @@ static struct page *stable_tree_search(struct page *page) } nid = get_kpfn_nid(page_to_pfn(page)); + root = root_stable_tree + nid; again: - new = &root_stable_tree[nid].rb_node; + new = &root->rb_node; parent = NULL; while (*new) { @@ -1219,7 +1225,7 @@ again: list_del(&page_node->list); DO_NUMA(page_node->nid = nid); rb_link_node(&page_node->node, parent, new); - rb_insert_color(&page_node->node, &root_stable_tree[nid]); + rb_insert_color(&page_node->node, root); get_page(page); return page; @@ -1227,11 +1233,10 @@ replace: if (page_node) { list_del(&page_node->list); DO_NUMA(page_node->nid = nid); - rb_replace_node(&stable_node->node, - &page_node->node, &root_stable_tree[nid]); + rb_replace_node(&stable_node->node, &page_node->node, root); get_page(page); } else { - rb_erase(&stable_node->node, &root_stable_tree[nid]); + rb_erase(&stable_node->node, root); page = NULL; } stable_node->head = &migrate_nodes; @@ -1250,13 +1255,15 @@ static struct stable_node *stable_tree_insert(struct page *kpage) { int nid; unsigned long kpfn; + struct rb_root *root; struct rb_node **new; struct rb_node *parent = NULL; struct stable_node *stable_node; kpfn = page_to_pfn(kpage); nid = get_kpfn_nid(kpfn); - new = &root_stable_tree[nid].rb_node; + root = root_stable_tree + nid; + new = &root->rb_node; while (*new) { struct page *tree_page; @@ -1295,7 +1302,7 @@ static struct stable_node *stable_tree_insert(struct page *kpage) set_page_stable_node(kpage, stable_node); DO_NUMA(stable_node->nid = nid); rb_link_node(&stable_node->node, parent, new); - rb_insert_color(&stable_node->node, &root_stable_tree[nid]); + rb_insert_color(&stable_node->node, root); return stable_node; } @@ -1325,7 +1332,7 @@ struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item, int nid; nid = get_kpfn_nid(page_to_pfn(page)); - root = &root_unstable_tree[nid]; + root = root_unstable_tree + nid; new = &root->rb_node; while (*new) { @@ -1422,7 +1429,7 @@ static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item) if (stable_node->head != &migrate_nodes && get_kpfn_nid(stable_node->kpfn) != NUMA(stable_node->nid)) { rb_erase(&stable_node->node, - &root_stable_tree[NUMA(stable_node->nid)]); + root_stable_tree + NUMA(stable_node->nid)); stable_node->head = &migrate_nodes; list_add(&stable_node->list, stable_node->head); } @@ -1574,7 +1581,7 @@ static struct rmap_item *scan_get_next_rmap_item(struct page **page) } } - for (nid = 0; nid < nr_node_ids; nid++) + for (nid = 0; nid < ksm_nr_node_ids; nid++) root_unstable_tree[nid] = RB_ROOT; spin_lock(&ksm_mmlist_lock); @@ -2094,8 +2101,8 @@ static void ksm_check_stable_tree(unsigned long start_pfn, struct rb_node *node; int nid; - for (nid = 0; nid < nr_node_ids; nid++) { - node = rb_first(&root_stable_tree[nid]); + for (nid = 0; nid < ksm_nr_node_ids; nid++) { + node = rb_first(root_stable_tree + nid); while (node) { stable_node = rb_entry(node, struct stable_node, node); if (stable_node->kpfn >= start_pfn && @@ -2105,7 +2112,7 @@ static void ksm_check_stable_tree(unsigned long start_pfn, * which is why we keep kpfn instead of page* */ remove_node_from_stable_tree(stable_node); - node = rb_first(&root_stable_tree[nid]); + node = rb_first(root_stable_tree + nid); } else node = rb_next(node); cond_resched(); @@ -2298,8 +2305,31 @@ static ssize_t merge_across_nodes_store(struct kobject *kobj, if (ksm_merge_across_nodes != knob) { if (ksm_pages_shared || remove_all_stable_nodes()) err = -EBUSY; - else + else if (root_stable_tree == one_stable_tree) { + struct rb_root *buf; + /* + * This is the first time that we switch away from the + * default of merging across nodes: must now allocate + * a buffer to hold as many roots as may be needed. + * Allocate stable and unstable together: + * MAXSMP NODES_SHIFT 10 will use 16kB. + */ + buf = kcalloc(nr_node_ids + nr_node_ids, + sizeof(*buf), GFP_KERNEL | __GFP_ZERO); + /* Let us assume that RB_ROOT is NULL is zero */ + if (!buf) + err = -ENOMEM; + else { + root_stable_tree = buf; + root_unstable_tree = buf + nr_node_ids; + /* Stable tree is empty but not the unstable */ + root_unstable_tree[0] = one_unstable_tree[0]; + } + } + if (!err) { ksm_merge_across_nodes = knob; + ksm_nr_node_ids = knob ? 1 : nr_node_ids; + } } mutex_unlock(&ksm_thread_mutex); @@ -2378,15 +2408,11 @@ static int __init ksm_init(void) { struct task_struct *ksm_thread; int err; - int nid; err = ksm_slab_init(); if (err) goto out; - for (nid = 0; nid < nr_node_ids; nid++) - root_stable_tree[nid] = RB_ROOT; - ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd"); if (IS_ERR(ksm_thread)) { printk(KERN_ERR "ksm: creating kthread failed\n"); -- cgit v0.10.2