x86: ensure percpu lpage doesn't consume too much vmalloc space

On extreme configuration (e.g. 32bit 32-way NUMA machine), lpage
percpu first chunk allocator can consume too much of vmalloc space.
Make it fall back to 4k allocator if the consumption goes over 20%.

[ Impact: add sanity check for lpage percpu first chunk allocator ]

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Jan Beulich <JBeulich@novell.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Ingo Molnar <mingo@elte.hu>

diff --git a/arch/x86/kernel/setup_percpu.c b/arch/x86/kernel/setup_percpu.c
index 165ebd5..29a3eef 100644 (file)
--- a/arch/x86/kernel/setup_percpu.c
+++ b/arch/x86/kernel/setup_percpu.c
@@ -163,9 +163,21 @@ static ssize_t __init setup_pcpu_lpage(size_t static_size, bool chosen)
        int i, j;
        ssize_t ret;
 
-       /* on non-NUMA, embedding is better */
-       if (!chosen && !pcpu_need_numa())
-               return -EINVAL;
+       if (!chosen) {
+               size_t vm_size = VMALLOC_END - VMALLOC_START;
+               size_t tot_size = num_possible_cpus() * PMD_SIZE;
+
+               /* on non-NUMA, embedding is better */
+               if (!pcpu_need_numa())
+                       return -EINVAL;
+
+               /* don't consume more than 20% of vmalloc area */
+               if (tot_size > vm_size / 5) {
+                       pr_info("PERCPU: too large chunk size %zuMB for "
+                               "large page remap\n", tot_size >> 20);
+                       return -EINVAL;
+               }
+       }
 
        /* need PSE */
        if (!cpu_has_pse) {