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pmap study: how to find a memory leak.

2011-11-17 17:28 465 查看

pmap is a good tool to report the memory map of a process. But how to make sure a process has memory leak, here is the tips:

1, if the virtual memory (VIRT) or writeable/private (‘pmap –d’ output) keeps increasing stably when you repeat the same operation, it should be have memory leak.

2, The RSS is just for your reference, it can’t used as the factor to detect memory leak.

3, although you call ‘free’ or ‘delete’, the virtual memory may not shrink immediately.

4, the same new operation may mapped to different [anon] virtual memory space. Here 1M was alloated to
000000001b56a000 and
00002ac25a77c000.

000000001b56a000
1156 12 12 rw---
[ anon ]

00002ac25a77c000
1040 16 16 rw---
[ anon ]

Test Code:

#include "stdio.h"
int global_i_init=0;
static int static_global_j=11;
int global_k;

int main () {
int tmp;
printf ("global_i_init: 0x%lx\n",&global_i_init );
printf ("global_k non_init : 0x%lx\n",&global_k );
printf ("static_global_j  : 0x%lx\n",&static_global_j );
printf ("stack i  : 0x%lx\n",&tmp );

getchar (); // step2
char *x= new char[100*1024];
printf ("data allocate 100k @0x%lx\n", x);
getchar();  // step3
char *x2= new char[1024*1024];
printf ("data allocate 1M i@0x%lx\n", x2);

getchar(); // step4
printf ("data write at x2[1024*1024-1] ");
x2[1024*1024-1]=0;

getchar(); // step5
printf ("data read at x2 ");
int j;
for (int i=0;i<1024*1024; i++)
j=x2[i];
getchar (); // step6
printf ("delete x2");
delete x2;

getchar ();  //step 7
printf ("delete x");
delete x;

getchar();  //step8

x2= new char[1024*1024];
printf ("data allocate 1M i@0x%lx\n", x2);

getchar ();
}

Program output:

ATCA48-0-0-1:/root-# ./a.out
global_i_init: 0x500cc0
global_k non_init : 0x500cc4
static_global_j  : 0x500cb8
stack i  : 0x7fff0120ab5c
data allocate 100k @0x1b56a010
data allocate 1M i@0x2ac25a77f010
data write at x2[1024*1024-1]
data read at x2
delete x2
delete x
data allocate 1M i@0x1b56a010

pmap -d output:

		mapped	writeable/private:	shared
STEP 1	init	19616K	236K	0
STEP 2	new 100k	19848K	468K	0
STEP 3	new 1M	20876K	1496K	0
STEP 4	write 1 byte	20876K	1496K	0
STEP 5	read 1M	20876K	1496K	0
STEP 6	delete 1M	19848K	468K	0
STEP 7	delete 100k	19848K	468K	0
STEP 8	new 1M	20772K	1392K	0

pmap -d conclusion:

1, mapped and writeable/private can reflect the memory variation.

2, delete or free may not decrease mapped or writeable/private immediately.

pmap -x output:

		Total kbytes	RSS	Dirty
STEP 1	init	19616	912	124
STEP 2	new 100k	19848	976	140
STEP 3	new 1M	20876	980	144
STEP 4	write 1 byte	20876	984	148
STEP 5	read 1M	20876	2004	148
STEP 6	delete 1M	19848	976	140
STEP 7	delete 100k	19848	980	140
STEP 8	new 1M	20772	984	144

		Address	kbytes	RSS	Dirty
STEP 1	init
STEP 2	new 100k	000000001b56a000	232	8	8
STEP 3	new 1M	000000001b56a000	232	8	8
STEP 4	write 1 byte	000000001b56a000	232	8	8
STEP 5	read 1M	000000001b56a000	232	8	8
STEP 6	delete 1M	000000001b56a000	232	8	8
STEP 7	delete 100k	000000001b56a000	232	8	8
STEP 8	new 1M	000000001b56a000	1156	12	12

		Address	kbytes	RSS	Dirty
STEP 1	init	00002ac25a77c000	12	12	12
STEP 2	new 100k	00002ac25a77c000	12	12	12
STEP 3	new 1M	00002ac25a77c000	1040	16	16
STEP 4	write 1 byte	00002ac25a77c000	1040	20	20
STEP 5	read 1M	00002ac25a77c000	1040	1040	20
STEP 6	delete 1M	00002ac25a77c000	12	12	12
STEP 7	delete 100k	00002ac25a77c000	12	12	12
STEP 8	new 1M	00002ac25a77c000	12	12	12

pmap -x conclusion:

1, although you used new(step 3), the OS didn't commit the memory page until you read (STEP5)or write(STEP4) that memory space.

pmap -x:

2, the new memory operation maybe happened on different Address range. like the first 1M allcation at
00002ac25a77c000, but the 2nd 1M allcation happened at 000000001b56a000

Final pmap -d:

Address           Kbytes Mode  Offset           Device    Mapping
0000000000400000       4 r-x-- 0000000000000000 008:00001 a.out
0000000000500000       4 rw--- 0000000000000000 008:00001 a.out
000000001b56a000    1156 rw--- 000000001b56a000 000:00000   [ anon ]
0000003677000000     112 r-x-- 0000000000000000 008:00001 ld-2.5.so
000000367721c000       4 r---- 000000000001c000 008:00001 ld-2.5.so
000000367721d000       4 rw--- 000000000001d000 008:00001 ld-2.5.so
0000003677400000    1336 r-x-- 0000000000000000 008:00001 libc-2.5.so
000000367754e000    2048 ----- 000000000014e000 008:00001 libc-2.5.so
000000367774e000      16 r---- 000000000014e000 008:00001 libc-2.5.so
0000003677752000       4 rw--- 0000000000152000 008:00001 libc-2.5.so
0000003677753000      20 rw--- 0000003677753000 000:00000   [ anon ]
0000003677c00000     520 r-x-- 0000000000000000 008:00001 libm-2.5.so
0000003677c82000    2044 ----- 0000000000082000 008:00001 libm-2.5.so
0000003677e81000       4 r---- 0000000000081000 008:00001 libm-2.5.so
0000003677e82000       4 rw--- 0000000000082000 008:00001 libm-2.5.so
0000003678c00000      52 r-x-- 0000000000000000 008:00001 libgcc_s-4.1.2-20080825.so.1
0000003678c0d000    2048 ----- 000000000000d000 008:00001 libgcc_s-4.1.2-20080825.so.1
0000003678e0d000       4 rw--- 000000000000d000 008:00001 libgcc_s-4.1.2-20080825.so.1
0000003679400000     920 r-x-- 0000000000000000 008:00001 libstdc++.so.6.0.8
00000036794e6000    2044 ----- 00000000000e6000 008:00001 libstdc++.so.6.0.8
00000036796e5000      24 r---- 00000000000e5000 008:00001 libstdc++.so.6.0.8
00000036796eb000      12 rw--- 00000000000eb000 008:00001 libstdc++.so.6.0.8
00000036796ee000      72 rw--- 00000036796ee000 000:00000   [ anon ]
00002ac25a76f000      16 rw--- 00002ac25a76f000 000:00000   [ anon ]
00002ac25a77c000      12 rw--- 00002ac25a77c000 000:00000   [ anon ]
00007fff011f8000      84 rw--- 00007ffffffe9000 000:00000   [ stack ]
00007fff013c2000      12 r-x-- 00007fff013c2000 000:00000   [ anon ]
ffffffffff600000    8192 ----- 0000000000000000 000:00000   [ anon ]
mapped: 20772K    writeable/private: 1392K    shared: 0K

Final pmap -x

Address           Kbytes     RSS   Dirty Mode   Mapping
0000000000400000       4       4       0 r-x--  a.out
0000000000500000       4       4       4 rw---  a.out
000000001b56a000    1156      12      12 rw---    [ anon ]
0000003677000000     112      96       0 r-x--  ld-2.5.so
000000367721c000       4       4       4 r----  ld-2.5.so
000000367721d000       4       4       4 rw---  ld-2.5.so
0000003677400000    1336     284       0 r-x--  libc-2.5.so
000000367754e000    2048       0       0 -----  libc-2.5.so
000000367774e000      16      16       8 r----  libc-2.5.so
0000003677752000       4       4       4 rw---  libc-2.5.so
0000003677753000      20      16      16 rw---    [ anon ]
0000003677c00000     520      20       0 r-x--  libm-2.5.so
0000003677c82000    2044       0       0 -----  libm-2.5.so
0000003677e81000       4       4       4 r----  libm-2.5.so
0000003677e82000       4       4       4 rw---  libm-2.5.so
0000003678c00000      52      16       0 r-x--  libgcc_s-4.1.2-20080825.so.1
0000003678c0d000    2048       0       0 -----  libgcc_s-4.1.2-20080825.so.1
0000003678e0d000       4       4       4 rw---  libgcc_s-4.1.2-20080825.so.1
0000003679400000     920     404       0 r-x--  libstdc++.so.6.0.8
00000036794e6000    2044       0       0 -----  libstdc++.so.6.0.8
00000036796e5000      24      24      20 r----  libstdc++.so.6.0.8
00000036796eb000      12      12      12 rw---  libstdc++.so.6.0.8
00000036796ee000      72       8       8 rw---    [ anon ]
00002ac25a76f000      16      16      16 rw---    [ anon ]
00002ac25a77c000      12      12      12 rw---    [ anon ]
00007fff011f8000      84      12      12 rw---    [ stack ]
00007fff013c2000      12       4       0 r-x--    [ anon ]
ffffffffff600000    8192       0       0 -----    [ anon ]
----------------  ------  ------  ------
total kB           20772     984     144

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