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Subject[PATCH 10/12] 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>
---
mm/ksm.c | 26 +++++++++++++++++++-------
1 file changed, 19 insertions(+), 7 deletions(-)
--- ksm9/mm/ksm.c 2009-08-02 13:50:41.000000000 +0100
+++ ksm10/mm/ksm.c 2009-08-02 13:50:48.000000000 +0100
@@ -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_a
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)
{
@@ -1464,6 +1469,11 @@ 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) \
@@ -1646,6 +1656,7 @@ static struct attribute_group ksm_attr_g
.attrs = ksm_attrs,
.name = "ksm",
};
+#endif /* CONFIG_SYSFS */

static int __init ksm_init(void)
{
@@ -1667,16 +1678,17 @@ 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:

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