Messages in this thread Patch in this message | | | Date | Wed, 30 Apr 2008 21:42:41 +0100 | From | Alan Cox <> | Subject | [PATCH 1/2] mm: Fix overcommit overflow |
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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@redhat.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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