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Message-Id: <20220803100530.1653496-1-xu.xin16@zte.con.cn>
Date: Wed, 3 Aug 2022 10:05:30 +0000
From: cgel.zte@...il.com
To: akpm@...ux-foundation.org
Cc: hughd@...gle.com, izik.eidus@...ellosystems.com,
willy@...radead.org, linux-kernel@...r.kernel.org,
linux-mm@...ck.org, xu xin <xu.xin16@....com.cn>,
CGEL <cgel.zte@...il.com>
Subject: [RFC PATCH 2/4] ksm: implement scan-enhanced algorithm of auto mode
From: xu xin <xu.xin16@....com.cn>
Implement the scan-enhanced algorithm of auto mode. In this algorithm,
after every time of scanning, if new ksm pages are obtained, it will
double pages_to_scan for the next scanning until the general
multiplying factor is not less than max_scanning_factor. If no new ksm
pages are obtained, then reset pages_to_scan to the default value.
We add the sysfs klob of max_scanning_factor to limit scanning factor's
excessive growth.
Signed-off-by: CGEL <cgel.zte@...il.com>
Signed-off-by: xu xin <xu.xin16@....com.cn>
---
mm/ksm.c | 88 ++++++++++++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 86 insertions(+), 2 deletions(-)
diff --git a/mm/ksm.c b/mm/ksm.c
index c80d908221a4..8acc893e4d61 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -131,6 +131,8 @@ struct mm_slot {
* @address: the next address inside that to be scanned
* @rmap_list: link to the next rmap to be scanned in the rmap_list
* @seqnr: count of completed full scans (needed when removing unstable node)
+ * @new_ksmpages_of_this_scanning: count of the new merged KSM pages in the
+ * current scanning of mm_lists (cleared after ksm_do_scan() ends)
*
* There is only the one ksm_scan instance of this cursor structure.
*/
@@ -139,6 +141,7 @@ struct ksm_scan {
unsigned long address;
struct rmap_item **rmap_list;
unsigned long seqnr;
+ unsigned long new_ksmpages_of_this_scanning;
};
/**
@@ -277,6 +280,20 @@ static unsigned int zero_checksum __read_mostly;
/* Whether to merge empty (zeroed) pages with actual zero pages */
static bool ksm_use_zero_pages __read_mostly;
+/*
+ * Work in auto-mode.
+ * Maximum number of multiplicative factor of pages_to_scan.
+ */
+static unsigned int ksm_max_scanning_factor = 32;
+
+/*
+ * Work in auto-mode.
+ * The multiplicative factor of pages_to_scan.
+ * Real pages to scan equals to the product of scanning_factor
+ * and pages_to_scan
+ */
+static unsigned int scanning_factor = 1;
+
#ifdef CONFIG_NUMA
/* Zeroed when merging across nodes is not allowed */
static unsigned int ksm_merge_across_nodes = 1;
@@ -2031,6 +2048,8 @@ static void stable_tree_append(struct rmap_item *rmap_item,
rmap_item->address |= STABLE_FLAG;
hlist_add_head(&rmap_item->hlist, &stable_node->hlist);
+ ksm_scan.new_ksmpages_of_this_scanning++;
+
if (rmap_item->hlist.next)
ksm_pages_sharing++;
else
@@ -2396,6 +2415,23 @@ static struct rmap_item *scan_get_next_rmap_item(struct page **page)
return NULL;
}
+/*
+ * enhance_scanning_factor():
+ * double the values of scanning_factor, but not more than
+ * ksm_max_scanning_factor.
+ */
+static inline void enhance_scanning_factor(void)
+{
+ scanning_factor = scanning_factor << 1;
+ if (scanning_factor > ksm_max_scanning_factor)
+ scanning_factor = ksm_max_scanning_factor;
+}
+
+static inline void reset_scanning_factor(void)
+{
+ scanning_factor = 1;
+}
+
/**
* ksm_do_scan - the ksm scanner main worker function.
* @scan_npages: number of pages we want to scan before we return.
@@ -2432,10 +2468,31 @@ static int ksm_scan_thread(void *nothing)
while (!kthread_should_stop()) {
mutex_lock(&ksm_thread_mutex);
wait_while_offlining();
- if (ksmd_should_run())
- ksm_do_scan(ksm_thread_pages_to_scan);
+ if (ksmd_should_run()) {
+ if (ksm_run & KSM_RUN_AUTO)
+ ksm_do_scan(ksm_thread_pages_to_scan * scanning_factor);
+ else
+ ksm_do_scan(ksm_thread_pages_to_scan);
+ }
mutex_unlock(&ksm_thread_mutex);
+ /*
+ * If there are new ksm pages after scanning, then we
+ * can enhance scanning_factor to improve ksm_thread's
+ * pages_to_scan to speed up scanning. Otherwaise, we
+ * reset scanning_factor to be one, so that to recover
+ * the normal state because there is greater probability
+ * of getting no new KsmPages in the next scanning.
+ */
+ if (ksm_run & KSM_RUN_AUTO) {
+ if (ksm_scan.new_ksmpages_of_this_scanning > 0)
+ enhance_scanning_factor();
+ else
+ reset_scanning_factor();
+
+ ksm_scan.new_ksmpages_of_this_scanning = 0;
+ }
+
try_to_freeze();
if (ksmd_should_run()) {
@@ -2952,6 +3009,32 @@ static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
}
KSM_ATTR(run);
+static ssize_t max_scanning_factor_show(struct kobject *kobj,
+ struct kobj_attribute *attr, char *buf)
+{
+ return sysfs_emit(buf, "%u\n", ksm_max_scanning_factor);
+}
+
+static ssize_t max_scanning_factor_store(struct kobject *kobj,
+ struct kobj_attribute *attr,
+ const char *buf, size_t count)
+{
+ unsigned int value;
+ int err;
+
+ err = kstrtouint(buf, 10, &value);
+ if (err)
+ return -EINVAL;
+
+ if (value < 1)
+ return -EINVAL;
+
+ ksm_max_scanning_factor = value;
+
+ return count;
+}
+KSM_ATTR(max_scanning_factor);
+
#ifdef CONFIG_NUMA
static ssize_t merge_across_nodes_show(struct kobject *kobj,
struct kobj_attribute *attr, char *buf)
@@ -3162,6 +3245,7 @@ static struct attribute *ksm_attrs[] = {
&sleep_millisecs_attr.attr,
&pages_to_scan_attr.attr,
&run_attr.attr,
+ &max_scanning_factor_attr.attr,
&pages_shared_attr.attr,
&pages_sharing_attr.attr,
&pages_unshared_attr.attr,
--
2.25.1
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