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SubjectRe: Linux 2.6.24.4+mmap with overcommit >= 1
On Wed, 30 Apr 2008 04:19:54 +0300
Sami Farin <safari-kernel@safari.iki.fi> wrote:

> I have arch x86_64, glibc-2.7.90-7 from Fedora.
> When I have vm.overcommit_memory == 1 or 2,
> mmap succeeds for really huge values.
> These ranges succeed (approximate):
> 8793870000000 - 17500387000000
> 26390387000000 - 35180387000000

Fun fun fun

This should fix strict overcommit (== 2) I think


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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