From: David Mosberger <davidm@napali.hpl.hp.com>
Below is a warmed up version of a patch originally done by Werner Almesberger
(see http://tinyurl.com/25zra) to replace the MAX_MAP_COUNT limit with a
sysctl variable. I thought this had gone into the tree a long time ago but
alas it has not and as luck would have it, the hard limit bit someone today
once again with a large app on a large machine.
Here is a small test app:
-----------------------------------------------------------------
#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>
int
main (int argc, char **argv)
{
long n = 0;
printf ("Starting mmap test...\n");
while (1)
if (mmap (0, 1, (n++ & 1) ? PROT_READ : PROT_WRITE,
MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE,
-1, 0) == MAP_FAILED)
{
printf ("Failed after %ld successful maps\n", n - 1);
exit (0);
}
return -1;
}
-----------------------------------------------------------------
After applying the patch, I was able to do 20,000,000 successful maps while
consuming about 3.6GB of memory (~ 180 bytes/map) which matches well enough
with the actual vm_area_struct size of 128 bytes. If I set the max_map_count
insanely high, the above test keeps running until we're out of memory and
then the OOM killer kicks in. Basically: no surprises.
---
25-akpm/Documentation/sysctl/vm.txt | 16 ++++++++++++++++
25-akpm/include/linux/sched.h | 4 +++-
25-akpm/include/linux/sysctl.h | 1 +
25-akpm/kernel/sysctl.c | 8 ++++++++
25-akpm/mm/mmap.c | 8 +++++---
5 files changed, 33 insertions(+), 4 deletions(-)
diff -puN Documentation/sysctl/vm.txt~max_map_count-sysctl Documentation/sysctl/vm.txt
--- 25/Documentation/sysctl/vm.txt~max_map_count-sysctl Mon Mar 29 16:33:25 2004
+++ 25-akpm/Documentation/sysctl/vm.txt Mon Mar 29 16:33:25 2004
@@ -22,6 +22,7 @@ Currently, these files are in /proc/sys/
- dirty_background_ratio
- dirty_expire_centisecs
- dirty_writeback_centisecs
+- max_map_count
- min_free_kbytes
==============================================================
@@ -77,6 +78,21 @@ for swap because we only cluster swap da
==============================================================
+max_map_count:
+
+This file contains the maximum number of memory map areas a process
+may have. Memory map areas are used as a side-effect of calling
+malloc, directly by mmap and mprotect, and also when loading shared
+libraries.
+
+While most applications need less than a thousand maps, certain
+programs, particularly malloc debuggers, may consume lots of them,
+e.g., up to one or two maps per allocation.
+
+The default value is 65536.
+
+==============================================================
+
min_free_kbytes:
This is used to force the Linux VM to keep a minimum number
diff -puN include/linux/sched.h~max_map_count-sysctl include/linux/sched.h
--- 25/include/linux/sched.h~max_map_count-sysctl Mon Mar 29 16:33:25 2004
+++ 25-akpm/include/linux/sched.h Mon Mar 29 16:33:25 2004
@@ -180,7 +180,9 @@ asmlinkage void schedule(void);
struct namespace;
/* Maximum number of active map areas.. This is a random (large) number */
-#define MAX_MAP_COUNT (65536)
+#define DEFAULT_MAX_MAP_COUNT 65536
+
+extern int sysctl_max_map_count;
#include <linux/aio.h>
diff -puN include/linux/sysctl.h~max_map_count-sysctl include/linux/sysctl.h
--- 25/include/linux/sysctl.h~max_map_count-sysctl Mon Mar 29 16:33:25 2004
+++ 25-akpm/include/linux/sysctl.h Mon Mar 29 16:34:45 2004
@@ -158,6 +158,7 @@ enum
VM_SWAPPINESS=19, /* Tendency to steal mapped memory */
VM_LOWER_ZONE_PROTECTION=20,/* Amount of protection of lower zones */
VM_MIN_FREE_KBYTES=21, /* Minimum free kilobytes to maintain */
+ VM_MAX_MAP_COUNT=22, /* int: Maximum number of mmaps/address-space */
};
diff -puN kernel/sysctl.c~max_map_count-sysctl kernel/sysctl.c
--- 25/kernel/sysctl.c~max_map_count-sysctl Mon Mar 29 16:33:25 2004
+++ 25-akpm/kernel/sysctl.c Mon Mar 29 16:34:33 2004
@@ -736,6 +736,14 @@ static ctl_table vm_table[] = {
.strategy = &sysctl_intvec,
.extra1 = &zero,
},
+ {
+ .ctl_name = VM_MAX_MAP_COUNT,
+ .procname = "max_map_count",
+ .data = &sysctl_max_map_count,
+ .maxlen = sizeof(sysctl_max_map_count),
+ .mode = 0644,
+ .proc_handler = &proc_dointvec
+ },
{ .ctl_name = 0 }
};
diff -puN mm/mmap.c~max_map_count-sysctl mm/mmap.c
--- 25/mm/mmap.c~max_map_count-sysctl Mon Mar 29 16:33:25 2004
+++ 25-akpm/mm/mmap.c Mon Mar 29 16:33:25 2004
@@ -54,10 +54,12 @@ pgprot_t protection_map[16] = {
int sysctl_overcommit_memory = 0; /* default is heuristic overcommit */
int sysctl_overcommit_ratio = 50; /* default is 50% */
+int sysctl_max_map_count = DEFAULT_MAX_MAP_COUNT;
atomic_t vm_committed_space = ATOMIC_INIT(0);
EXPORT_SYMBOL(sysctl_overcommit_memory);
EXPORT_SYMBOL(sysctl_overcommit_ratio);
+EXPORT_SYMBOL(sysctl_max_map_count);
EXPORT_SYMBOL(vm_committed_space);
/*
@@ -516,7 +518,7 @@ unsigned long do_mmap_pgoff(struct file
return -EINVAL;
/* Too many mappings? */
- if (mm->map_count > MAX_MAP_COUNT)
+ if (mm->map_count > sysctl_max_map_count)
return -ENOMEM;
/* Obtain the address to map to. we verify (or select) it and ensure
@@ -1202,7 +1204,7 @@ int split_vma(struct mm_struct * mm, str
struct vm_area_struct *new;
struct address_space *mapping = NULL;
- if (mm->map_count >= MAX_MAP_COUNT)
+ if (mm->map_count >= sysctl_max_map_count)
return -ENOMEM;
new = kmem_cache_alloc(vm_area_cachep, SLAB_KERNEL);
@@ -1380,7 +1382,7 @@ unsigned long do_brk(unsigned long addr,
> current->rlim[RLIMIT_AS].rlim_cur)
return -ENOMEM;
- if (mm->map_count > MAX_MAP_COUNT)
+ if (mm->map_count > sysctl_max_map_count)
return -ENOMEM;
if (security_vm_enough_memory(len >> PAGE_SHIFT))
_