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Message-ID: <alpine.LNX.2.00.1302210027450.17843@eggly.anvils>
Date: Thu, 21 Feb 2013 00:29:15 -0800 (PST)
From: Hugh Dickins <hughd@...gle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
cc: Mel Gorman <mgorman@...e.de>, Petr Holasek <pholasek@...hat.com>,
Andrea Arcangeli <aarcange@...hat.com>,
Izik Eidus <izik.eidus@...ellosystems.com>,
linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: [PATCH 7/7] 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 <hughd@...gle.com>
---
mm/ksm.c | 72 ++++++++++++++++++++++++++++++++++++-----------------
1 file changed, 49 insertions(+), 23 deletions(-)
--- mmotm.orig/mm/ksm.c 2013-02-20 22:50:10.540032454 -0800
+++ mmotm/mm/ksm.c 2013-02-20 23:21:28.908077096 -0800
@@ -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_mil
#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
@@ -506,7 +510,7 @@ static void remove_node_from_stable_tree
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);
}
@@ -642,7 +646,7 @@ static void remove_rmap_item_from_tree(s
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;
}
@@ -740,7 +744,7 @@ 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);
@@ -1148,6 +1152,7 @@ static struct page *try_to_merge_two_pag
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;
@@ -1161,8 +1166,9 @@ static struct page *stable_tree_search(s
}
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) {
@@ -1217,7 +1223,7 @@ 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;
@@ -1225,11 +1231,10 @@ 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;
@@ -1248,13 +1253,15 @@ static struct stable_node *stable_tree_i
{
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;
@@ -1293,7 +1300,7 @@ static struct stable_node *stable_tree_i
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;
}
@@ -1323,7 +1330,7 @@ struct rmap_item *unstable_tree_search_i
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) {
@@ -1420,7 +1427,7 @@ static void cmp_and_merge_page(struct pa
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);
}
@@ -1572,7 +1579,7 @@ static struct rmap_item *scan_get_next_r
}
}
- 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);
@@ -2089,8 +2096,8 @@ static void ksm_check_stable_tree(unsign
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 &&
@@ -2100,7 +2107,7 @@ static void ksm_check_stable_tree(unsign
* 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();
@@ -2293,8 +2300,31 @@ static ssize_t merge_across_nodes_store(
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);
@@ -2373,15 +2403,11 @@ 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");
--
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