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Message-ID: <20080430214241.4313e9ca@core>
Date: Wed, 30 Apr 2008 21:42:41 +0100
From: Alan Cox <alan@...rguk.ukuu.org.uk>
To: akpm@...l.org, linux-kernel@...r.kernel.org,
linux-mm@...r.kernel.org
Subject: [PATCH 1/2] mm: Fix overcommit overflow
Sami Farin reported an overflow in the overcommit handling on 64bit boxes.
We use atomic_t for page counting which is fine on 32bit but on 64bit
overflows. We can use atomic64_t but there is a problem - most heavy
users of zero overcommit are embedded people whose 64bit atomics are
really slow and expensive operations. Thus we use a few defines to flip
32 or 64bit according to the size of a long
(Split into two diffs to keep ownership correct)
Signed-off-by: Alan Cox <alan@...hat.com>
diff -u --new-file --recursive --exclude-from /usr/src/exclude linux.vanilla-2.6.25-mm1/include/linux/mman.h linux-2.6.25-mm1/include/linux/mman.h
--- linux.vanilla-2.6.25-mm1/include/linux/mman.h 2008-04-28 11:35:21.000000000 +0100
+++ linux-2.6.25-mm1/include/linux/mman.h 2008-04-30 11:21:10.000000000 +0100
@@ -15,16 +15,31 @@
#include <asm/atomic.h>
+/* 32bit platforms have a virtual address space in pages we
+ can fit into an atomic_t. We want to avoid atomic64_t on
+ such boxes as it is often expensive and most strict overcommit
+ users turn out to be embedded low power processors */
+
+#if (BITS_PER_LONG == 32)
+#define vm_atomic_t atomic_t
+#define vm_atomic_read atomic_read
+#define vm_atomic_add atomic_add
+#else
+#define vm_atomic_t atomic64_t
+#define vm_atomic_read atomic64_read
+#define vm_atomic_add atomic64_add
+#endif
+
extern int sysctl_overcommit_memory;
extern int sysctl_overcommit_ratio;
-extern atomic_t vm_committed_space;
+extern vm_atomic_t vm_committed_space;
#ifdef CONFIG_SMP
extern void vm_acct_memory(long pages);
#else
static inline void vm_acct_memory(long pages)
{
- atomic_add(pages, &vm_committed_space);
+ vm_atomic_add(pages, &vm_committed_space);
}
#endif
diff -u --new-file --recursive --exclude-from /usr/src/exclude linux.vanilla-2.6.25-mm1/mm/mmap.c linux-2.6.25-mm1/mm/mmap.c
--- linux.vanilla-2.6.25-mm1/mm/mmap.c 2008-04-28 11:36:52.000000000 +0100
+++ linux-2.6.25-mm1/mm/mmap.c 2008-04-30 11:17:03.000000000 +0100
@@ -80,7 +80,7 @@
int sysctl_overcommit_memory = OVERCOMMIT_GUESS; /* heuristic overcommit */
int sysctl_overcommit_ratio = 50; /* default is 50% */
int sysctl_max_map_count __read_mostly = DEFAULT_MAX_MAP_COUNT;
-atomic_t vm_committed_space = ATOMIC_INIT(0);
+vm_atomic_t vm_committed_space = ATOMIC_INIT(0);
/*
* Check that a process has enough memory to allocate a new virtual
@@ -177,7 +177,7 @@
* cast `allowed' as a signed long because vm_committed_space
* sometimes has a negative value
*/
- if (atomic_read(&vm_committed_space) < (long)allowed)
+ if (vm_atomic_read(&vm_committed_space) < (long)allowed)
return 0;
error:
vm_unacct_memory(pages);
diff -u --new-file --recursive --exclude-from /usr/src/exclude linux.vanilla-2.6.25-mm1/mm/swap.c linux-2.6.25-mm1/mm/swap.c
--- linux.vanilla-2.6.25-mm1/mm/swap.c 2008-04-28 11:36:52.000000000 +0100
+++ linux-2.6.25-mm1/mm/swap.c 2008-04-30 11:18:05.000000000 +0100
@@ -503,7 +503,7 @@
local = &__get_cpu_var(committed_space);
*local += pages;
if (*local > ACCT_THRESHOLD || *local < -ACCT_THRESHOLD) {
- atomic_add(*local, &vm_committed_space);
+ vm_atomic_add(*local, &vm_committed_space);
*local = 0;
}
preempt_enable();
--
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