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Message-Id: <20220812101202.41533-1-xu.xin16@zte.com.cn>
Date: Fri, 12 Aug 2022 10:12:02 +0000
From: cgel.zte@...il.com
To: akpm@...ux-foundation.org, willy@...radead.org
Cc: hughd@...gle.com, izik.eidus@...ellosystems.com,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
xu.xin16@....com.cn, CGEL <cgel.zte@...il.com>
Subject: [PATCH v2 2/5] ksm: implement scan-enhanced algorithm
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 | 100 +++++++++++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 98 insertions(+), 2 deletions(-)
diff --git a/mm/ksm.c b/mm/ksm.c
index c80d908221a4..f416f168a6da 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -131,6 +131,10 @@ 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: count of the new merged KSM pages in the current scanning
+ * of mm_lists (cleared after every turn of ksm_do_scan() ends)
+ * @prev_ksmpages: the record of the new merged KSM pages in the last turn of
+ * scanning by ksm_do_scan().
*
* There is only the one ksm_scan instance of this cursor structure.
*/
@@ -139,6 +143,8 @@ struct ksm_scan {
unsigned long address;
struct rmap_item **rmap_list;
unsigned long seqnr;
+ unsigned long new_ksmpages;
+ unsigned long prev_ksmpages;
};
/**
@@ -277,6 +283,19 @@ 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.
+ * The multiplicative factor of pages_to_scan.
+ * Real pages to scan equals to the product of scanning_factor
+ * and pages_to_scan
+ */
+#define INIT_SCANNING_FACTOR 1
+static unsigned int scanning_factor = INIT_SCANNING_FACTOR;
+
+/* The upper limit of scanning_factor */
+#define DEFAULT_MAX_SCANNING_FACTOR 16
+static unsigned int max_scanning_factor = DEFAULT_MAX_SCANNING_FACTOR;
+
#ifdef CONFIG_NUMA
/* Zeroed when merging across nodes is not allowed */
static unsigned int ksm_merge_across_nodes = 1;
@@ -2031,6 +2050,8 @@ 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++;
+
if (rmap_item->hlist.next)
ksm_pages_sharing++;
else
@@ -2422,6 +2443,41 @@ static int ksmd_should_run(void)
return 0;
}
+/*
+ * Work in auto mode, the scan-enhanced algorithm.
+ * current_factor: the current scanning_factor.
+ * return: the scanning_factor caculated by scan-enhanced algorithm.
+ */
+static unsigned int scan_enhanced_algorithm(unsigned int current_factor)
+{
+ unsigned int next_factor;
+ unsigned int max, min;
+
+ /*
+ * The calculation is divied into three cases as follows:
+ *
+ * Case 1: when new_ksmpages > prev_ksmpages * 1/2, get the
+ * next factor by double the current factor.
+ * Case 2: when 0 < new_ksmpages < prev_ksmpages * 1/2, keep
+ * the factor unchanged.
+ * Case 3: when new_ksmpages equals 0, then get the next
+ * factor by halfing the current factor.
+ */
+ max = READ_ONCE(max_scanning_factor);
+ min = INIT_SCANNING_FACTOR;
+ if (ksm_scan.new_ksmpages * 2 > ksm_scan.prev_ksmpages) {
+ next_factor = current_factor << 1; /* Doubling */
+ if (next_factor > max)
+ next_factor = max;
+ } else if (ksm_scan.new_ksmpages == 0) {
+ next_factor = current_factor >> 1; /* Halfing */
+ next_factor = next_factor < min ? min : next_factor;
+ } else
+ next_factor = current_factor;
+
+ return next_factor;
+}
+
static int ksm_scan_thread(void *nothing)
{
unsigned int sleep_ms;
@@ -2432,8 +2488,19 @@ 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);
+
+ scanning_factor = scan_enhanced_algorithm(scanning_factor);
+ /*
+ * Reset ksm_scan.new_ksmpages after
+ * updating scanning_factor by scan_enhanced_algorithm.
+ */
+ ksm_scan.new_ksmpages = 0;
+ } else
+ ksm_do_scan(ksm_thread_pages_to_scan);
+ }
mutex_unlock(&ksm_thread_mutex);
try_to_freeze();
@@ -2904,6 +2971,34 @@ static ssize_t pages_to_scan_store(struct kobject *kobj,
}
KSM_ATTR(pages_to_scan);
+static ssize_t max_scanning_factor_show(struct kobject *kobj,
+ struct kobj_attribute *attr, char *buf)
+{
+ return sysfs_emit(buf, "%u\n", 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, max;
+ int err;
+
+ err = kstrtouint(buf, 10, &value);
+ if (err)
+ return -EINVAL;
+
+ max = totalram_pages() / ksm_thread_pages_to_scan;
+
+ if (value < 1 && value > max)
+ return -EINVAL;
+
+ max_scanning_factor = value;
+
+ return count;
+}
+KSM_ATTR(max_scanning_factor);
+
static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
char *buf)
{
@@ -3161,6 +3256,7 @@ KSM_ATTR_RO(full_scans);
static struct attribute *ksm_attrs[] = {
&sleep_millisecs_attr.attr,
&pages_to_scan_attr.attr,
+ &max_scanning_factor_attr.attr,
&run_attr.attr,
&pages_shared_attr.attr,
&pages_sharing_attr.attr,
--
2.25.1
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