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Subject[PATCH] [RFC] KSM: numa awareness sysfs knob
Date
Introduce a new sysfs knob /sys/kernel/mm/ksm/max_node_dist, whose
value will be used as the limitation for node distance of merged pages.

Signed-off-by: Petr Holasek <pholasek@redhat.com>
---
Documentation/vm/ksm.txt | 4 ++
mm/ksm.c | 122 +++++++++++++++++++++++++++++++++++----------
2 files changed, 99 insertions(+), 27 deletions(-)
diff --git a/Documentation/vm/ksm.txt b/Documentation/vm/ksm.txt
index b392e49..b882140 100644
--- a/Documentation/vm/ksm.txt
+++ b/Documentation/vm/ksm.txt
@@ -58,6 +58,10 @@ sleep_millisecs - how many milliseconds ksmd should sleep before next scan
e.g. "echo 20 > /sys/kernel/mm/ksm/sleep_millisecs"
Default: 20 (chosen for demonstration purposes)

+max_node_dist - maximum node distance between two pages which could be
+ merged.
+ Default: 255 (without any limitations)
+
run - set 0 to stop ksmd from running but keep merged pages,
set 1 to run ksmd e.g. "echo 1 > /sys/kernel/mm/ksm/run",
set 2 to stop ksmd and unmerge all pages currently merged,
diff --git a/mm/ksm.c b/mm/ksm.c
index 310544a..ea33040 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -36,6 +36,7 @@
#include <linux/hash.h>
#include <linux/freezer.h>
#include <linux/oom.h>
+#include <linux/numa.h>

#include <asm/tlbflush.h>
#include "internal.h"
@@ -120,6 +121,7 @@ struct stable_node {
struct rb_node node;
struct hlist_head hlist;
unsigned long kpfn;
+ int nid;
};

/**
@@ -153,8 +155,8 @@ struct rmap_item {
#define STABLE_FLAG 0x200 /* is listed from the stable tree */

/* The stable and unstable tree heads */
-static struct rb_root root_stable_tree = RB_ROOT;
static struct rb_root root_unstable_tree = RB_ROOT;
+static struct rb_root root_stable_tree[MAX_NUMNODES] = { RB_ROOT, };

#define MM_SLOTS_HASH_SHIFT 10
#define MM_SLOTS_HASH_HEADS (1 << MM_SLOTS_HASH_SHIFT)
@@ -189,6 +191,9 @@ static unsigned int ksm_thread_pages_to_scan = 100;
/* Milliseconds ksmd should sleep between batches */
static unsigned int ksm_thread_sleep_millisecs = 20;

+/* Maximum distance of nodes in which pages are merged */
+static unsigned int ksm_node_distance = 255;
+
#define KSM_RUN_STOP 0
#define KSM_RUN_MERGE 1
#define KSM_RUN_UNMERGE 2
@@ -302,6 +307,25 @@ static inline int in_stable_tree(struct rmap_item *rmap_item)
return rmap_item->address & STABLE_FLAG;
}

+#ifdef CONFIG_NUMA
+static inline int node_dist(int from, int to)
+{
+ int dist = node_distance(from, to);
+
+ return dist == -1 ? 0 : dist;
+}
+#else
+static inline int node_dist(int from, int to)
+{
+ return 0;
+}
+#endif
+
+static inline int page_distance(struct page *from, struct page *to)
+{
+ return node_dist(page_to_nid(from), page_to_nid(to));
+}
+
/*
* ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's
* page tables after it has passed through ksm_exit() - which, if necessary,
@@ -458,7 +482,8 @@ static void remove_node_from_stable_tree(struct stable_node *stable_node)
cond_resched();
}

- rb_erase(&stable_node->node, &root_stable_tree);
+ rb_erase(&stable_node->node, &root_stable_tree[stable_node->nid]);
+ printk(KERN_DEBUG "Node erased from tree %d\n", stable_node->nid);
free_stable_node(stable_node);
}

@@ -960,6 +985,9 @@ static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item,
{
int err;

+ if (page_distance(page, tree_page) > ksm_node_distance)
+ return NULL;
+
err = try_to_merge_with_ksm_page(rmap_item, page, NULL);
if (!err) {
err = try_to_merge_with_ksm_page(tree_rmap_item,
@@ -983,10 +1011,11 @@ static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item,
* This function returns the stable tree node of identical content if found,
* NULL otherwise.
*/
-static struct page *stable_tree_search(struct page *page)
+static struct page *stable_tree_search(struct page *page, int tree_nid)
{
- struct rb_node *node = root_stable_tree.rb_node;
+ struct rb_node *node = root_stable_tree[tree_nid].rb_node;
struct stable_node *stable_node;
+ int page_nid = page_to_nid(page);

stable_node = page_stable_node(page);
if (stable_node) { /* ksm page forked */
@@ -994,6 +1023,10 @@ static struct page *stable_tree_search(struct page *page)
return page;
}

+ /* Pages are too far for merge */
+ if (node_dist(tree_nid, page_nid) > ksm_node_distance)
+ return NULL;
+
while (node) {
struct page *tree_page;
int ret;
@@ -1028,7 +1061,8 @@ static struct page *stable_tree_search(struct page *page)
*/
static struct stable_node *stable_tree_insert(struct page *kpage)
{
- struct rb_node **new = &root_stable_tree.rb_node;
+ int nid = page_to_nid(kpage);
+ struct rb_node **new = &root_stable_tree[nid].rb_node;
struct rb_node *parent = NULL;
struct stable_node *stable_node;

@@ -1065,12 +1099,14 @@ static struct stable_node *stable_tree_insert(struct page *kpage)
return NULL;

rb_link_node(&stable_node->node, parent, new);
- rb_insert_color(&stable_node->node, &root_stable_tree);
+ rb_insert_color(&stable_node->node, &root_stable_tree[nid]);

INIT_HLIST_HEAD(&stable_node->hlist);

stable_node->kpfn = page_to_pfn(kpage);
+ stable_node->nid = nid;
set_page_stable_node(kpage, stable_node);
+ printk(KERN_DEBUG "Stable node was inserted into tree %d\n", nid);

return stable_node;
}
@@ -1173,27 +1209,32 @@ static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
struct rmap_item *tree_rmap_item;
struct page *tree_page = NULL;
struct stable_node *stable_node;
- struct page *kpage;
+ struct page *kpage = NULL;
unsigned int checksum;
int err;
+ int i;
+ int nid = page_to_nid(page);

remove_rmap_item_from_tree(rmap_item);

/* We first start with searching the page inside the stable tree */
- kpage = stable_tree_search(page);
- if (kpage) {
- err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
- if (!err) {
- /*
- * The page was successfully merged:
- * add its rmap_item to the stable tree.
- */
- lock_page(kpage);
- stable_tree_append(rmap_item, page_stable_node(kpage));
- unlock_page(kpage);
+ for (i = 0; i < MAX_NUMNODES; i++) {
+ if (node_distance(i, nid) <= ksm_node_distance)
+ kpage = stable_tree_search(page, nid);
+ if (kpage) {
+ err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
+ if (!err) {
+ /*
+ * The page was successfully merged:
+ * add its rmap_item to the stable tree.
+ */
+ lock_page(kpage);
+ stable_tree_append(rmap_item, page_stable_node(kpage));
+ unlock_page(kpage);
+ }
+ put_page(kpage);
+ return;
}
- put_page(kpage);
- return;
}

/*
@@ -1764,15 +1805,18 @@ static struct stable_node *ksm_check_stable_tree(unsigned long start_pfn,
unsigned long end_pfn)
{
struct rb_node *node;
+ int i;

- for (node = rb_first(&root_stable_tree); node; node = rb_next(node)) {
- struct stable_node *stable_node;
+ for (i = 0; i < MAX_NUMNODES; i++)
+ for (node = rb_first(&root_stable_tree[i]); node; node = rb_next(node)) {
+ struct stable_node *stable_node;
+
+ stable_node = rb_entry(node, struct stable_node, node);
+ if (stable_node->kpfn >= start_pfn &&
+ stable_node->kpfn < end_pfn)
+ return stable_node;
+ }

- stable_node = rb_entry(node, struct stable_node, node);
- if (stable_node->kpfn >= start_pfn &&
- stable_node->kpfn < end_pfn)
- return stable_node;
- }
return NULL;
}

@@ -1922,6 +1966,29 @@ static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
}
KSM_ATTR(run);

+static ssize_t max_node_dist_show(struct kobject *kobj,
+ struct kobj_attribute *attr, char *buf)
+{
+ return sprintf(buf, "%u\n", ksm_node_distance);
+}
+
+static ssize_t max_node_dist_store(struct kobject *kobj,
+ struct kobj_attribute *attr,
+ const char *buf, size_t count)
+{
+ int err;
+ unsigned long node_dist;
+
+ err = kstrtoul(buf, 10, &node_dist);
+ if (err || node_dist > 255)
+ return -EINVAL;
+
+ ksm_node_distance = node_dist;
+
+ return count;
+}
+KSM_ATTR(max_node_dist);
+
static ssize_t pages_shared_show(struct kobject *kobj,
struct kobj_attribute *attr, char *buf)
{
@@ -1976,6 +2043,7 @@ static struct attribute *ksm_attrs[] = {
&pages_unshared_attr.attr,
&pages_volatile_attr.attr,
&full_scans_attr.attr,
+ &max_node_dist_attr.attr,
NULL,
};

--
1.7.6.4


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