ksm: sysfs and defaults

At present KSM is just a waste of space if you don't have CONFIG_SYSFS=y
to provide the /sys/kernel/mm/ksm files to tune and activate it.

Make KSM depend on SYSFS?  Could do, but it might be better to provide
some defaults so that KSM works out-of-the-box, ready for testers to
madvise MADV_MERGEABLE, even without SYSFS.

Though anyone serious is likely to want to retune the numbers to their
taste once they have experience; and whether these settings ever reach
2.6.32 can be discussed along the way.

Save 1kB from tiny kernels by #ifdef'ing the SYSFS side of it.

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

1 files changed, 19 insertions, 7 deletions

diff --git a/mm/ksm.c b/mm/ksm.c
index 92034eb47eba..3bd54ce9eb38 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -163,18 +163,18 @@ static unsigned long ksm_pages_unshared;
 static unsigned long ksm_rmap_items;
 
 /* Limit on the number of unswappable pages used */
-static unsigned long ksm_max_kernel_pages;
+static unsigned long ksm_max_kernel_pages = 2000;
 
 /* Number of pages ksmd should scan in one batch */
-static unsigned int ksm_thread_pages_to_scan;
+static unsigned int ksm_thread_pages_to_scan = 200;
 
 /* Milliseconds ksmd should sleep between batches */
-static unsigned int ksm_thread_sleep_millisecs;
+static unsigned int ksm_thread_sleep_millisecs = 20;
 
 #define KSM_RUN_STOP    0
 #define KSM_RUN_MERGE   1
 #define KSM_RUN_UNMERGE 2
-static unsigned int ksm_run;
+static unsigned int ksm_run = KSM_RUN_MERGE;
 
 static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait);
 static DEFINE_MUTEX(ksm_thread_mutex);
@@ -506,6 +506,10 @@ static int unmerge_ksm_pages(struct vm_area_struct *vma,
         return err;
 }
 
+#ifdef CONFIG_SYSFS
+/*
+ * Only called through the sysfs control interface:
+ */
 static int unmerge_and_remove_all_rmap_items(void)
 {
         struct mm_slot *mm_slot;
@@ -563,6 +567,7 @@ error:
         spin_unlock(&ksm_mmlist_lock);
         return err;
 }
+#endif /* CONFIG_SYSFS */
 
 static u32 calc_checksum(struct page *page)
 {
@@ -1454,6 +1459,11 @@ void __ksm_exit(struct mm_struct *mm)
         }
 }
 
+#ifdef CONFIG_SYSFS
+/*
+ * This all compiles without CONFIG_SYSFS, but is a waste of space.
+ */
+
 #define KSM_ATTR_RO(_name) \
         static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
 #define KSM_ATTR(_name) \
@@ -1636,6 +1646,7 @@ static struct attribute_group ksm_attr_group = {
         .attrs = ksm_attrs,
         .name = "ksm",
 };
+#endif /* CONFIG_SYSFS */
 
 static int __init ksm_init(void)
 {
@@ -1657,16 +1668,17 @@ static int __init ksm_init(void)
                 goto out_free2;
         }
 
+#ifdef CONFIG_SYSFS
         err = sysfs_create_group(mm_kobj, &ksm_attr_group);
         if (err) {
                 printk(KERN_ERR "ksm: register sysfs failed\n");
-                goto out_free3;
+                kthread_stop(ksm_thread);
+                goto out_free2;
         }
+#endif /* CONFIG_SYSFS */
 
         return 0;
 
-out_free3:
-        kthread_stop(ksm_thread);
 out_free2:
         mm_slots_hash_free();
 out_free1: