当长度大于4GB的mmap失败 [英] mmap fails when length is larger than 4GB
问题描述
（正确的code在更新5'）
(The correct code is in 'Update 5')
我试图的范围内0x100000000存储器在该例C code映射到0x200000000
I tried to map a range of memory from 0x100000000 to 0x200000000 in this example C code:
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <sys/mman.h>
int main(void)
{
uint64_t* rr_addr = 0;
uint64_t i = 17179869184;
printf("\nsizeof(size_t): %llu\n", sizeof(size_t));
printf("(uint64_t)0x100000000: %llx\n", (uint64_t)0x100000000);
printf("1L << 33: %llx\n", 1L << 33);
rr_addr = mmap((void*)i, (1UL << 33), PROT_READ|PROT_WRITE, MAP_ANON|MAP_PRIVATE, -1, 0);
printf("rr_addr: %p, %llu \n", rr_addr, rr_addr);
if (rr_addr == MAP_FAILED) {
perror("mmap error");
}
return 0;
}
在不同的系统（Linux，GCC），我得到不同的结果：
On different systems (Linux, gcc), I get different results:
结果1：
sizeof(size_t): 8
(uint64_t)0x100000000: 100000000
1L << 33: 200000000
rr_addr: 0xffffffffffffffff, 18446744073709551615
mmap error: Cannot allocate memory
系统信息（Fedora 14的）：
System info (Fedora 14):
Linux localhost.localdomain 2.6.35.10-74.fc14.x86_64 #1 SMP Thu Dec 23 16:04:50 UTC 2010 x86_64 x86_64 x86_64 GNU/Linux
gcc (GCC) 4.5.1 20100924 (Red Hat 4.5.1-4)
glibc: 2.12.90-21
结果2：
sizeof(size_t): 8
(uint64_t)0x100000000: 100000000
1L << 33: 200000000
rr_addr: 0x400000000, 17179869184
系统信息（Fedora 12的）：
System info (Fedora 12):
Linux wiles 2.6.32.13 #2 SMP Fri Sep 10 01:29:43 HKT 2010 x86_64 x86_64 x86_64 GNU/Linux
gcc (GCC) 4.4.4 20100630 (Red Hat 4.4.4-10)
glibc verison: 2.11.2-1
我期待结果2。也许有什么毛病我的code。
I expect "Result 2". Maybe there is something wrong with my code.
请帮助我。
更新1 ：将errno如果MMAP失败打印出来
Update 1: errno is printed out if mmap fails.
更新3 ：改变MMAP调用这些行后：
Update 3: after changing the mmap call to these lines:
char *cmd[20];
sprintf(cmd, "pmap -x %i", getpid());
printf("%s\n", cmd);
system(cmd);
rr_addr = mmap((void*)i, (1UL << 33), PROT_READ|PROT_WRITE, MAP_ANON|MAP_PRIVATE, -1, 0);
printf("%s\n", cmd);
system(cmd);
结果：
sizeof(size_t): 8
(uint64_t)0x100000000: 100000000
1L << 33: 200000000
pmap -x 5618
5618: ./test
Address Kbytes RSS Dirty Mode Mapping
0000000000400000 4 4 0 r-x-- test
0000000000600000 4 4 4 rw--- test
00007f1cc941e000 1640 280 0 r-x-- libc-2.12.90.so
00007f1cc95b8000 2044 0 0 ----- libc-2.12.90.so
00007f1cc97b7000 16 16 16 r---- libc-2.12.90.so
00007f1cc97bb000 4 4 4 rw--- libc-2.12.90.so
00007f1cc97bc000 24 16 16 rw--- [ anon ]
00007f1cc97c2000 132 108 0 r-x-- ld-2.12.90.so
00007f1cc99c6000 12 12 12 rw--- [ anon ]
00007f1cc99e0000 8 8 8 rw--- [ anon ]
00007f1cc99e2000 4 4 4 r---- ld-2.12.90.so
00007f1cc99e3000 4 4 4 rw--- ld-2.12.90.so
00007f1cc99e4000 4 4 4 rw--- [ anon ]
00007fffa0da8000 132 8 8 rw--- [ stack ]
00007fffa0dff000 4 4 0 r-x-- [ anon ]
ffffffffff600000 4 0 0 r-x-- [ anon ]
---------------- ------ ------ ------
total kB 4040 476 80
pmap -x 5618
5618: ./test
Address Kbytes RSS Dirty Mode Mapping
0000000000400000 4 4 0 r-x-- test
0000000000600000 4 4 4 rw--- test
00007f1cc941e000 1640 280 0 r-x-- libc-2.12.90.so
00007f1cc95b8000 2044 0 0 ----- libc-2.12.90.so
00007f1cc97b7000 16 16 16 r---- libc-2.12.90.so
00007f1cc97bb000 4 4 4 rw--- libc-2.12.90.so
00007f1cc97bc000 24 16 16 rw--- [ anon ]
00007f1cc97c2000 132 108 0 r-x-- ld-2.12.90.so
00007f1cc99c6000 12 12 12 rw--- [ anon ]
00007f1cc99e0000 8 8 8 rw--- [ anon ]
00007f1cc99e2000 4 4 4 r---- ld-2.12.90.so
00007f1cc99e3000 4 4 4 rw--- ld-2.12.90.so
00007f1cc99e4000 4 4 4 rw--- [ anon ]
00007fffa0da8000 132 8 8 rw--- [ stack ]
00007fffa0dff000 4 4 0 r-x-- [ anon ]
ffffffffff600000 4 0 0 r-x-- [ anon ]
---------------- ------ ------ ------
total kB 4040 476 80
rr_addr: 0xffffffffffffffff, 18446744073709551615
mmap error: Cannot allocate memory
更新4 ：添加系统（-m的ulimit -v）;只是打电话MMAP之前：
的ulimit的输出是：
Update 4: add "system("ulimit -m -v");" just before calling mmap: The output of ulimit is:
max memory size (kbytes, -m) unlimited
virtual memory (kbytes, -v) unlimited
另一输出是相同的更新3'（仍然失败）除外的PID
The other output is the same as 'Update 3' (still fails) except the pid.
更新5 ：更新code这两个系统的工作原理：
Update 5: the updated code which works on both systems:
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <sys/mman.h>
int main(void)
{
uint64_t* rr_addr = 0;
uint64_t i = 17179869184;
uint64_t len = 0;
char cmd[20];
printf("\nsizeof(size_t): %llu\n", sizeof(size_t));
len = (1UL << 32);
printf("len: %llx\n", len);
snprintf(cmd, sizeof cmd, "pmap -x %i", getpid());
printf("%s\n", cmd);
system(cmd);
system("ulimit -m -v");
rr_addr = mmap((void*)i, len, PROT_READ|PROT_WRITE, MAP_ANON|MAP_PRIVATE|MAP_NORESERVE, -1, 0);
printf("%s\n", cmd);
system(cmd);
printf("rr_addr: %p, %llu \n", rr_addr, rr_addr);
if (rr_addr == MAP_FAILED) {
perror("mmap error");
}
return 0;
}
正确的答案被@caf给出：添加MAP_NORESERVE标志的mmap解决了这个问题。原因详细信息可在咖啡馆的答案。非常感谢CAF与所有这些给予善意的帮助！
The right answer is given by @caf: adding the MAP_NORESERVE flag to mmap solves this problem. Details of the reason are in caf's answer. Thanks a lot caf and all these give kind help!
推荐答案
如果你实际上并不比换8G的配置显著多，那么大的映射可能会失败。
If you do not actually have significantly more than 8G of swap configured, then that large mapping is likely to fail.
您可以在 MAP_NORESERVE 标志添加到的mmap（）来告诉它不保留任何交换空间的映射锋线。
You can add the MAP_NORESERVE flag to mmap() to tell it not to reserve any swap space for the mapping up front.
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