ksm: more on default values

Adjust the max_kernel_pages default to a quarter of totalram_pages,
instead of nr_free_buffer_pages() / 4: the KSM pages themselves come from
highmem, and even on a 16GB PAE machine, 4GB of KSM pages would only be
pinning 32MB of lowmem with their rmap_items, so no need for the more
obscure calculation (nor for its own special init function).

There is no way for the user to switch KSM on if CONFIG_SYSFS is not
enabled, so in that case default run to KSM_RUN_MERGE.

Update KSM Documentation and Kconfig to reflect the new defaults.

Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: 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>

2 files changed, 7 insertions, 7 deletions

diff --git a/mm/Kconfig b/mm/Kconfig
index edd300aca173..57963c6063d1 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -224,7 +224,9 @@ config KSM
           the many instances by a single resident page with that content, so
           saving memory until one or another app needs to modify the content.
           Recommended for use with KVM, or with other duplicative applications.
-          See Documentation/vm/ksm.txt for more information.
+          See Documentation/vm/ksm.txt for more information: KSM is inactive
+          until a program has madvised that an area is MADV_MERGEABLE, and
+          root has set /sys/kernel/mm/ksm/run to 1 (if CONFIG_SYSFS is set).
 
 config DEFAULT_MMAP_MIN_ADDR
         int "Low address space to protect from user allocation"
diff --git a/mm/ksm.c b/mm/ksm.c
index f7edac356f46..bef1af4f77e3 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -184,11 +184,6 @@ static DEFINE_SPINLOCK(ksm_mmlist_lock);
                 sizeof(struct __struct), __alignof__(struct __struct),\
                 (__flags), NULL)
 
-static void __init ksm_init_max_kernel_pages(void)
-{
-        ksm_max_kernel_pages = nr_free_buffer_pages() / 4;
-}
-
 static int __init ksm_slab_init(void)
 {
         rmap_item_cache = KSM_KMEM_CACHE(rmap_item, 0);
@@ -1673,7 +1668,7 @@ static int __init ksm_init(void)
         struct task_struct *ksm_thread;
         int err;
 
-        ksm_init_max_kernel_pages();
+        ksm_max_kernel_pages = totalram_pages / 4;
 
         err = ksm_slab_init();
         if (err)
@@ -1697,6 +1692,9 @@ static int __init ksm_init(void)
                 kthread_stop(ksm_thread);
                 goto out_free2;
         }
+#else
+        ksm_run = KSM_RUN_MERGE;        /* no way for user to start it */
+
 #endif /* CONFIG_SYSFS */
 
         return 0;