[PATCH] Root reservations for strict overcommit

This was on my TODO list for a while and it turns out someone already fixed
the armwaving overcommit mode for the same problem.  It is easy to get into
a situation where you have no overcommit and nothing can be done because
there is no memory to clean up the stable but non-useful state of the
machine.

The fix is trivial and duplicated from the armwaving overcommit code path.
The last 3% of the memory can be claimed by root processes only.  It isn't
a cure but it does seem to solve the real world problems - at least
providing you have enough memory for 3% to be useful 8).

Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/security/commoncap.c b/security/commoncap.c
index 28956930460a5112581cde7a68588eba3dbdf23f..217bbab2701e9398beee40351f439ac5b73d6c08 100644 (file)
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -357,6 +357,11 @@ int cap_vm_enough_memory(long pages)
 
        allowed = (totalram_pages - hugetlb_total_pages())
                * sysctl_overcommit_ratio / 100;
+       /*
+        * Leave the last 3% for root
+        */
+       if (!capable(CAP_SYS_ADMIN))
+               allowed -= allowed / 32;
        allowed += total_swap_pages;
 
        if (atomic_read(&vm_committed_space) < allowed)