On Mon, Apr 08, 2013 at 01:37:12PM -0700, Andrew Morton wrote:
> On Mon, 8 Apr 2013 15:07:38 -0400 Andrew Shewmaker <agshew@xxxxxxxxx> wrote:
>
> > This patch alters the admin and user reserves of the previous patches
> > in this series when memory is added or removed.
> >
> > If memory is added and the reserves have been eliminated or increased above
> > the default max, then we'll trust the admin.
> >
> > If memory is removed and there isn't enough free memory, then we
> > need to reset the reserves.
> >
> > Otherwise keep the reserve set by the admin.
> >
> > The reserve reset code is the same as the reserve initialization code.
> >
> > Does this sound reasonable to other people? I figured that hot removal
> > with too large of memory in the reserves was the most important case
> > to get right.
>
> Seems reasonable to me.
>
> I don't understand the magic numbers 1<<13 and 1<<17. How could I?
> Please add comments explaining how and why these were chosen.
The v9 patch I posted has this too, but here is a patch against
yesterday's mmotm.
diff --git a/mm/mmap.c b/mm/mmap.c
index 099a16d..cee7e74 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -3119,6 +3119,13 @@ module_init(init_admin_reserve)
/*
* Reinititalise user and admin reserves if memory is added or removed.
*
+ * The default user reserve max is 128MB, and the default max for the
+ * admin reserve is 8MB. These are usually, but not always, enough to
+ * enable recovery from a memory hogging process using login/sshd, a shell,
+ * and tools like top. It may make sense to increase or even disable the
+ * reserve depending on the existence of swap or variations in the recovery
+ * tools. So, the admin may have changed them.
+ *
* If memory is added and the reserves have been eliminated or increased above
* the default max, then we'll trust the admin.
*
@@ -3134,10 +3141,16 @@ static int reserve_mem_notifier(struct notifier_block *nb,
switch (action) {
case MEM_ONLINE:
+ /*
+ * Default max is 128MB. Leave alone if modified by operator.
+ */
tmp = sysctl_user_reserve_kbytes;
if (0 < tmp && tmp < (1UL << 17))
init_user_reserve();
+ /*
+ * Default max is 8MB. Leave alone if modified by operator.
+ */
tmp = sysctl_admin_reserve_kbytes;
if (0 < tmp && tmp < (1UL << 13))
init_admin_reserve();
--
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