ksm: remove unswappable max_kernel_pages

Now that ksm pages are swappable, and the known holes plugged, remove
mention of unswappable kernel pages from KSM documentation and comments.

Remove the totalram_pages/4 initialization of max_kernel_pages.  In fact,
remove max_kernel_pages altogether - we can reinstate it if removal turns
out to break someone's script; but if we later want to limit KSM's memory
usage, limiting the stable nodes would not be an effective approach.

Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/ksm.c

@@ -179,9 +179,6 @@ static unsigned long ksm_pages_unshared;
 /* The number of rmap_items in use: to calculate pages_volatile */
 static unsigned long ksm_rmap_items;
 
-/* Limit on the number of unswappable pages used */
-static unsigned long ksm_max_kernel_pages;
-
 /* Number of pages ksmd should scan in one batch */
 static unsigned int ksm_thread_pages_to_scan = 100;
 
@@ -943,14 +940,6 @@ static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item,
 {
 	int err;
 
-	/*
-	 * The number of nodes in the stable tree
-	 * is the number of kernel pages that we hold.
-	 */
-	if (ksm_max_kernel_pages &&
-	    ksm_max_kernel_pages <= ksm_pages_shared)
-		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,
@@ -1850,8 +1839,8 @@ static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
 	/*
 	 * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
 	 * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
-	 * breaking COW to free the unswappable pages_shared (but leaves
-	 * mm_slots on the list for when ksmd may be set running again).
+	 * breaking COW to free the pages_shared (but leaves mm_slots
+	 * on the list for when ksmd may be set running again).
 	 */
 
 	mutex_lock(&ksm_thread_mutex);
@@ -1876,29 +1865,6 @@ static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
 }
 KSM_ATTR(run);
 
-static ssize_t max_kernel_pages_store(struct kobject *kobj,
-				      struct kobj_attribute *attr,
-				      const char *buf, size_t count)
-{
-	int err;
-	unsigned long nr_pages;
-
-	err = strict_strtoul(buf, 10, &nr_pages);
-	if (err)
-		return -EINVAL;
-
-	ksm_max_kernel_pages = nr_pages;
-
-	return count;
-}
-
-static ssize_t max_kernel_pages_show(struct kobject *kobj,
-				     struct kobj_attribute *attr, char *buf)
-{
-	return sprintf(buf, "%lu\n", ksm_max_kernel_pages);
-}
-KSM_ATTR(max_kernel_pages);
-
 static ssize_t pages_shared_show(struct kobject *kobj,
 				 struct kobj_attribute *attr, char *buf)
 {
@@ -1948,7 +1914,6 @@ static struct attribute *ksm_attrs[] = {
 	&sleep_millisecs_attr.attr,
 	&pages_to_scan_attr.attr,
 	&run_attr.attr,
-	&max_kernel_pages_attr.attr,
 	&pages_shared_attr.attr,
 	&pages_sharing_attr.attr,
 	&pages_unshared_attr.attr,
@@ -1968,8 +1933,6 @@ static int __init ksm_init(void)
 	struct task_struct *ksm_thread;
 	int err;
 
-	ksm_max_kernel_pages = totalram_pages / 4;
-
 	err = ksm_slab_init();
 	if (err)
 		goto out;