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Subjectreplace MAX_MAP_COUNT with /proc/sys/vm/max_map_count
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.

Please consider for inclusion.

Thanks,

--david

===== Documentation/sysctl/vm.txt 1.11 vs edited =====
--- 1.11/Documentation/sysctl/vm.txt Tue Jan 20 17:58:52 2004
+++ edited/Documentation/sysctl/vm.txt Fri Mar 26 21:04:47 2004
@@ -22,6 +22,7 @@
- dirty_background_ratio
- dirty_expire_centisecs
- dirty_writeback_centisecs
+- max_map_count
- min_free_kbytes

==============================================================
@@ -74,6 +75,21 @@
The number of pages the kernel reads in at once is equal to
2 ^ page-cluster. Values above 2 ^ 5 don't make much sense
for swap because we only cluster swap data in 32-page groups.
+
+==============================================================
+
+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.

==============================================================

===== include/linux/sched.h 1.170 vs edited =====
--- 1.170/include/linux/sched.h Fri Mar 19 20:31:17 2004
+++ edited/include/linux/sched.h Fri Mar 26 21:16:57 2004
@@ -179,7 +179,9 @@
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>

===== include/linux/sysctl.h 1.60 vs edited =====
--- 1.60/include/linux/sysctl.h Wed Mar 10 12:07:02 2004
+++ edited/include/linux/sysctl.h Fri Mar 26 21:06:40 2004
@@ -158,6 +158,7 @@
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 active map areas per address-space */
};


===== kernel/sysctl.c 1.58 vs edited =====
--- 1.58/kernel/sysctl.c Wed Mar 24 10:52:11 2004
+++ edited/kernel/sysctl.c Fri Mar 26 21:14:53 2004
@@ -736,6 +736,14 @@
.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 }
};

===== mm/mmap.c 1.99 vs edited =====
--- 1.99/mm/mmap.c Mon Mar 15 22:50:13 2004
+++ edited/mm/mmap.c Fri Mar 26 21:14:40 2004
@@ -54,10 +54,12 @@

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);

/*
@@ -512,7 +514,7 @@
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
@@ -1197,7 +1199,7 @@
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);
@@ -1375,7 +1377,7 @@
> 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))
-
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