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>

1 files changed, 3 insertions, 1 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"