Skip to content

Commit

Permalink
ksm: allocate roots when needed
Browse files Browse the repository at this point in the history 
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@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Petr Holasek <pholasek@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Izik Eidus <izik.eidus@ravellosystems.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
  • Loading branch information
@torvalds
Hugh Dickins authored and torvalds committed Feb 24, 2013
1 parent 56f3180 commit ef53d16
Showing 1 changed file with 49 additions and 23 deletions.
72 changes: 49 additions & 23 deletions mm/ksm.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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);
Expand Down Expand Up @@ -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
Expand Down Expand Up @@ -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);
}

Expand Down Expand Up @@ -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;
}
Expand Down Expand Up @@ -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);
Expand Down Expand Up @@ -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;
Expand All @@ -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) {
Expand Down Expand Up @@ -1219,19 +1225,18 @@ static struct page *stable_tree_search(struct page *page)
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;

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;
Expand All @@ -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;
Expand Down Expand Up @@ -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;
}
Expand Down Expand Up @@ -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) {
Expand Down Expand Up @@ -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);
}
Expand Down Expand Up @@ -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);
Expand Down Expand Up @@ -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 &&
Expand All @@ -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();
Expand Down Expand Up @@ -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);

Expand Down Expand Up @@ -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");
Expand Down

0 comments on commit ef53d16

Please sign in to comment.