1 Demonstrations of memleak. 2 3 4 memleak traces and matches memory allocation and deallocation requests, and 5 collects call stacks for each allocation. memleak can then print a summary 6 of which call stacks performed allocations that weren't subsequently freed. 7 For example: 8 9 # ./memleak -p $(pidof allocs) 10 Attaching to pid 5193, Ctrl+C to quit. 11 [11:16:33] Top 2 stacks with outstanding allocations: 12 80 bytes in 5 allocations from stack 13 main+0x6d [allocs] 14 __libc_start_main+0xf0 [libc-2.21.so] 15 16 [11:16:34] Top 2 stacks with outstanding allocations: 17 160 bytes in 10 allocations from stack 18 main+0x6d [allocs] 19 __libc_start_main+0xf0 [libc-2.21.so] 20 21 22 Each entry printed is a set of allocations that originate from the same call 23 stack, and that weren't freed yet. The number of bytes and number of allocs 24 are followed by the call stack, top to bottom, of the allocation site. 25 26 As time goes on, it becomes apparent that the main function in the allocs 27 process is leaking memory, 16 bytes at a time. Fortunately, you don't have to 28 inspect each allocation individually -- you get a nice summary of which stack 29 is responsible for a large leak. 30 31 Occasionally, you do want the individual allocation details. Perhaps the same 32 stack is allocating various sizes and you want to confirm which sizes are 33 prevalent. Use the -a switch: 34 35 # ./memleak -p $(pidof allocs) -a 36 Attaching to pid 5193, Ctrl+C to quit. 37 [11:16:33] Top 2 stacks with outstanding allocations: 38 addr = 948cd0 size = 16 39 addr = 948d10 size = 16 40 addr = 948d30 size = 16 41 addr = 948cf0 size = 16 42 64 bytes in 4 allocations from stack 43 main+0x6d [allocs] 44 __libc_start_main+0xf0 [libc-2.21.so] 45 46 [11:16:34] Top 2 stacks with outstanding allocations: 47 addr = 948d50 size = 16 48 addr = 948cd0 size = 16 49 addr = 948d10 size = 16 50 addr = 948d30 size = 16 51 addr = 948cf0 size = 16 52 addr = 948dd0 size = 16 53 addr = 948d90 size = 16 54 addr = 948db0 size = 16 55 addr = 948d70 size = 16 56 addr = 948df0 size = 16 57 160 bytes in 10 allocations from stack 58 main+0x6d [allocs] 59 __libc_start_main+0xf0 [libc-2.21.so] 60 61 62 When using the -p switch, memleak traces the libc allocations of a particular 63 process. Without this switch, kernel allocations are traced instead. 64 For example: 65 66 # ./memleak 67 Attaching to kernel allocators, Ctrl+C to quit. 68 ... 69 248 bytes in 4 allocations from stack 70 bpf_prog_load [kernel] 71 sys_bpf [kernel] 72 73 328 bytes in 1 allocations from stack 74 perf_mmap [kernel] 75 mmap_region [kernel] 76 do_mmap [kernel] 77 vm_mmap_pgoff [kernel] 78 sys_mmap_pgoff [kernel] 79 sys_mmap [kernel] 80 81 464 bytes in 1 allocations from stack 82 traceprobe_command [kernel] 83 traceprobe_probes_write [kernel] 84 probes_write [kernel] 85 __vfs_write [kernel] 86 vfs_write [kernel] 87 sys_write [kernel] 88 entry_SYSCALL_64_fastpath [kernel] 89 90 8192 bytes in 1 allocations from stack 91 alloc_and_copy_ftrace_hash.constprop.59 [kernel] 92 ftrace_set_hash [kernel] 93 ftrace_set_filter_ip [kernel] 94 arm_kprobe [kernel] 95 enable_kprobe [kernel] 96 kprobe_register [kernel] 97 perf_trace_init [kernel] 98 perf_tp_event_init [kernel] 99 100 101 Here you can see that arming the kprobe to which our eBPF program is attached 102 consumed 8KB of memory. Loading the BPF program also consumed a couple hundred 103 bytes (in bpf_prog_load). 104 105 memleak stores each allocated block along with its size, timestamp, and the 106 stack that allocated it. When the block is deleted, this information is freed 107 to reduce the memory overhead. 108 109 To avoid false positives, allocations younger than a certain age (500ms by 110 default) are not printed. To change this threshold, use the -o switch. 111 112 By default, memleak prints its output every 5 seconds. To change this 113 interval, pass the interval as a positional parameter to memleak. You can 114 also control the number of times the output will be printed before exiting. 115 For example: 116 117 # ./memleak 1 10 118 119 ... will print the outstanding allocation statistics every second, for ten 120 times, and then exit. 121 122 memleak may introduce considerable overhead if your application or kernel is 123 allocating and freeing memory at a very high rate. In that case, you can 124 control the overhead by sampling every N-th allocation. For example, to sample 125 roughly 10% of the allocations and print the outstanding allocations every 5 126 seconds, 3 times before quitting: 127 128 # ./memleak -p $(pidof allocs) -s 10 5 3 129 Attaching to pid 2614, Ctrl+C to quit. 130 [11:16:33] Top 2 stacks with outstanding allocations: 131 16 bytes in 1 allocations from stack 132 main+0x6d [allocs] 133 __libc_start_main+0xf0 [libc-2.21.so] 134 135 [11:16:38] Top 2 stacks with outstanding allocations: 136 16 bytes in 1 allocations from stack 137 main+0x6d [allocs] 138 __libc_start_main+0xf0 [libc-2.21.so] 139 140 [11:16:43] Top 2 stacks with outstanding allocations: 141 32 bytes in 2 allocations from stack 142 main+0x6d [allocs] 143 __libc_start_main+0xf0 [libc-2.21.so] 144 145 Note that even though the application leaks 16 bytes of memory every second, 146 the report (printed every 5 seconds) doesn't "see" all the allocations because 147 of the sampling rate applied. 148 149 150 USAGE message: 151 152 # ./memleak -h 153 usage: memleak.py [-h] [-p PID] [-t] [-a] [-o OLDER] [-c COMMAND] 154 [--combined-only] [-s SAMPLE_RATE] [-T TOP] [-z MIN_SIZE] 155 [-Z MAX_SIZE] [-O OBJ] 156 [interval] [count] 157 158 Trace outstanding memory allocations that weren't freed. 159 Supports both user-mode allocations made with libc functions and kernel-mode 160 allocations made with kmalloc/kmem_cache_alloc/get_free_pages and corresponding 161 memory release functions. 162 163 positional arguments: 164 interval interval in seconds to print outstanding allocations 165 count number of times to print the report before exiting 166 167 optional arguments: 168 -h, --help show this help message and exit 169 -p PID, --pid PID the PID to trace; if not specified, trace kernel 170 allocs 171 -t, --trace print trace messages for each alloc/free call 172 -a, --show-allocs show allocation addresses and sizes as well as call 173 stacks 174 -o OLDER, --older OLDER 175 prune allocations younger than this age in 176 milliseconds 177 -c COMMAND, --command COMMAND 178 execute and trace the specified command 179 --combined-only show combined allocation statistics only 180 -s SAMPLE_RATE, --sample-rate SAMPLE_RATE 181 sample every N-th allocation to decrease the overhead 182 -T TOP, --top TOP display only this many top allocating stacks (by size) 183 -z MIN_SIZE, --min-size MIN_SIZE 184 capture only allocations larger than this size 185 -Z MAX_SIZE, --max-size MAX_SIZE 186 capture only allocations smaller than this size 187 -O OBJ, --obj OBJ attach to allocator functions in the specified object 188 189 EXAMPLES: 190 191 ./memleak -p $(pidof allocs) 192 Trace allocations and display a summary of "leaked" (outstanding) 193 allocations every 5 seconds 194 ./memleak -p $(pidof allocs) -t 195 Trace allocations and display each individual allocator function call 196 ./memleak -ap $(pidof allocs) 10 197 Trace allocations and display allocated addresses, sizes, and stacks 198 every 10 seconds for outstanding allocations 199 ./memleak -c "./allocs" 200 Run the specified command and trace its allocations 201 ./memleak 202 Trace allocations in kernel mode and display a summary of outstanding 203 allocations every 5 seconds 204 ./memleak -o 60000 205 Trace allocations in kernel mode and display a summary of outstanding 206 allocations that are at least one minute (60 seconds) old 207 ./memleak -s 5 208 Trace roughly every 5th allocation, to reduce overhead 209
