[PATCH] reduced and tunable swappiness

/proc/sys/vm/swappiness controls the VM's tendency to unmap pages and to
swap things out.

100 -> basically current 2.5 behaviour
0 -> not very swappy at all

The mechanism which is used to control swappiness is: to be reluctant
to bring mapped pages onto the inactive list.  Prefer to reclaim
pagecache instead.

The control for that mechanism is as follows:

- If there is a large amount of mapped memory in the machine, we
  prefer to bring mapped pages onto the inactive list.

- If page reclaim is under distress (more scanning is happening) then
  prefer to bring mapped pages onto the inactive list.  This is
  basically the 2.4 algorithm, really.

- If the /proc/sys/vm/swappiness control is high then prefer to bring
  mapped pages onto the inactive list.

The implementation is simple: calculate the above three things as
percentages and add them up.  If that's over 100% then start reclaiming
mapped pages.

The `proportion of mapped memory' is downgraded so that we don't swap
just because a lot of memory is mapped into pagetables - we still need
some VM distress before starting to swap that memory out.

For a while I was adding a little bias so that we prefer to unmap
file-backed memory before swapping out anon memory.  Because usually
file backed memory can be evicted and reestablished with one I/O, not
two.  It was unmapping executable text too easily, so here I just treat
them equally.

1 files changed, 3 insertions, 0 deletions

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 53d13c96fbf2..3b49efc1c523 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -311,6 +311,9 @@ static ctl_table vm_table[] = {
 	{ VM_NR_PDFLUSH_THREADS, "nr_pdflush_threads",
 	  &nr_pdflush_threads, sizeof nr_pdflush_threads,
 	  0444 /* read-only*/, NULL, &proc_dointvec},
+	{VM_SWAPPINESS, "swappiness", &vm_swappiness, sizeof(vm_swappiness),
+	 0644, NULL, &proc_dointvec_minmax, &sysctl_intvec, NULL, &zero,
+	 &one_hundred },
 #ifdef CONFIG_HUGETLB_PAGE
 	 {VM_HUGETLB_PAGES, "nr_hugepages", &htlbpage_max, sizeof(int), 0644, NULL, 
 	  &proc_dointvec},