| Demonstrations of memleak. |
| |
| |
| memleak traces and matches memory allocation and deallocation requests, and |
| collects call stacks for each allocation. memleak can then print a summary |
| of which call stacks performed allocations that weren't subsequently freed. |
| For example: |
| |
| # ./memleak -p $(pidof allocs) |
| Attaching to pid 5193, Ctrl+C to quit. |
| [11:16:33] Top 2 stacks with outstanding allocations: |
| 80 bytes in 5 allocations from stack |
| main+0x6d [allocs] |
| __libc_start_main+0xf0 [libc-2.21.so] |
| |
| [11:16:34] Top 2 stacks with outstanding allocations: |
| 160 bytes in 10 allocations from stack |
| main+0x6d [allocs] |
| __libc_start_main+0xf0 [libc-2.21.so] |
| |
| |
| Each entry printed is a set of allocations that originate from the same call |
| stack, and that weren't freed yet. The number of bytes and number of allocs |
| are followed by the call stack, top to bottom, of the allocation site. |
| |
| As time goes on, it becomes apparent that the main function in the allocs |
| process is leaking memory, 16 bytes at a time. Fortunately, you don't have to |
| inspect each allocation individually -- you get a nice summary of which stack |
| is responsible for a large leak. |
| |
| Occasionally, you do want the individual allocation details. Perhaps the same |
| stack is allocating various sizes and you want to confirm which sizes are |
| prevalent. Use the -a switch: |
| |
| # ./memleak -p $(pidof allocs) -a |
| Attaching to pid 5193, Ctrl+C to quit. |
| [11:16:33] Top 2 stacks with outstanding allocations: |
| addr = 948cd0 size = 16 |
| addr = 948d10 size = 16 |
| addr = 948d30 size = 16 |
| addr = 948cf0 size = 16 |
| 64 bytes in 4 allocations from stack |
| main+0x6d [allocs] |
| __libc_start_main+0xf0 [libc-2.21.so] |
| |
| [11:16:34] Top 2 stacks with outstanding allocations: |
| addr = 948d50 size = 16 |
| addr = 948cd0 size = 16 |
| addr = 948d10 size = 16 |
| addr = 948d30 size = 16 |
| addr = 948cf0 size = 16 |
| addr = 948dd0 size = 16 |
| addr = 948d90 size = 16 |
| addr = 948db0 size = 16 |
| addr = 948d70 size = 16 |
| addr = 948df0 size = 16 |
| 160 bytes in 10 allocations from stack |
| main+0x6d [allocs] |
| __libc_start_main+0xf0 [libc-2.21.so] |
| |
| |
| When using the -p switch, memleak traces the libc allocations of a particular |
| process. Without this switch, kernel allocations are traced instead. |
| For example: |
| |
| # ./memleak |
| Attaching to kernel allocators, Ctrl+C to quit. |
| ... |
| 248 bytes in 4 allocations from stack |
| bpf_prog_load [kernel] |
| sys_bpf [kernel] |
| |
| 328 bytes in 1 allocations from stack |
| perf_mmap [kernel] |
| mmap_region [kernel] |
| do_mmap [kernel] |
| vm_mmap_pgoff [kernel] |
| sys_mmap_pgoff [kernel] |
| sys_mmap [kernel] |
| |
| 464 bytes in 1 allocations from stack |
| traceprobe_command [kernel] |
| traceprobe_probes_write [kernel] |
| probes_write [kernel] |
| __vfs_write [kernel] |
| vfs_write [kernel] |
| sys_write [kernel] |
| entry_SYSCALL_64_fastpath [kernel] |
| |
| 8192 bytes in 1 allocations from stack |
| alloc_and_copy_ftrace_hash.constprop.59 [kernel] |
| ftrace_set_hash [kernel] |
| ftrace_set_filter_ip [kernel] |
| arm_kprobe [kernel] |
| enable_kprobe [kernel] |
| kprobe_register [kernel] |
| perf_trace_init [kernel] |
| perf_tp_event_init [kernel] |
| |
| |
| Here you can see that arming the kprobe to which our eBPF program is attached |
| consumed 8KB of memory. Loading the BPF program also consumed a couple hundred |
| bytes (in bpf_prog_load). |
| |
| memleak stores each allocated block along with its size, timestamp, and the |
| stack that allocated it. When the block is deleted, this information is freed |
| to reduce the memory overhead. |
| |
| To avoid false positives, allocations younger than a certain age (500ms by |
| default) are not printed. To change this threshold, use the -o switch. |
| |
| By default, memleak prints its output every 5 seconds. To change this |
| interval, pass the interval as a positional parameter to memleak. You can |
| also control the number of times the output will be printed before exiting. |
| For example: |
| |
| # ./memleak 1 10 |
| |
| ... will print the outstanding allocation statistics every second, for ten |
| times, and then exit. |
| |
| memleak may introduce considerable overhead if your application or kernel is |
| allocating and freeing memory at a very high rate. In that case, you can |
| control the overhead by sampling every N-th allocation. For example, to sample |
| roughly 10% of the allocations and print the outstanding allocations every 5 |
| seconds, 3 times before quitting: |
| |
| # ./memleak -p $(pidof allocs) -s 10 5 3 |
| Attaching to pid 2614, Ctrl+C to quit. |
| [11:16:33] Top 2 stacks with outstanding allocations: |
| 16 bytes in 1 allocations from stack |
| main+0x6d [allocs] |
| __libc_start_main+0xf0 [libc-2.21.so] |
| |
| [11:16:38] Top 2 stacks with outstanding allocations: |
| 16 bytes in 1 allocations from stack |
| main+0x6d [allocs] |
| __libc_start_main+0xf0 [libc-2.21.so] |
| |
| [11:16:43] Top 2 stacks with outstanding allocations: |
| 32 bytes in 2 allocations from stack |
| main+0x6d [allocs] |
| __libc_start_main+0xf0 [libc-2.21.so] |
| |
| Note that even though the application leaks 16 bytes of memory every second, |
| the report (printed every 5 seconds) doesn't "see" all the allocations because |
| of the sampling rate applied. |
| |
| |
| USAGE message: |
| |
| # ./memleak -h |
| usage: memleak.py [-h] [-p PID] [-t] [-a] [-o OLDER] [-c COMMAND] |
| [--combined-only] [-s SAMPLE_RATE] [-T TOP] [-z MIN_SIZE] |
| [-Z MAX_SIZE] [-O OBJ] |
| [interval] [count] |
| |
| Trace outstanding memory allocations that weren't freed. |
| Supports both user-mode allocations made with libc functions and kernel-mode |
| allocations made with kmalloc/kmem_cache_alloc/get_free_pages and corresponding |
| memory release functions. |
| |
| positional arguments: |
| interval interval in seconds to print outstanding allocations |
| count number of times to print the report before exiting |
| |
| optional arguments: |
| -h, --help show this help message and exit |
| -p PID, --pid PID the PID to trace; if not specified, trace kernel |
| allocs |
| -t, --trace print trace messages for each alloc/free call |
| -a, --show-allocs show allocation addresses and sizes as well as call |
| stacks |
| -o OLDER, --older OLDER |
| prune allocations younger than this age in |
| milliseconds |
| -c COMMAND, --command COMMAND |
| execute and trace the specified command |
| --combined-only show combined allocation statistics only |
| -s SAMPLE_RATE, --sample-rate SAMPLE_RATE |
| sample every N-th allocation to decrease the overhead |
| -T TOP, --top TOP display only this many top allocating stacks (by size) |
| -z MIN_SIZE, --min-size MIN_SIZE |
| capture only allocations larger than this size |
| -Z MAX_SIZE, --max-size MAX_SIZE |
| capture only allocations smaller than this size |
| -O OBJ, --obj OBJ attach to allocator functions in the specified object |
| |
| EXAMPLES: |
| |
| ./memleak -p $(pidof allocs) |
| Trace allocations and display a summary of "leaked" (outstanding) |
| allocations every 5 seconds |
| ./memleak -p $(pidof allocs) -t |
| Trace allocations and display each individual allocator function call |
| ./memleak -ap $(pidof allocs) 10 |
| Trace allocations and display allocated addresses, sizes, and stacks |
| every 10 seconds for outstanding allocations |
| ./memleak -c "./allocs" |
| Run the specified command and trace its allocations |
| ./memleak |
| Trace allocations in kernel mode and display a summary of outstanding |
| allocations every 5 seconds |
| ./memleak -o 60000 |
| Trace allocations in kernel mode and display a summary of outstanding |
| allocations that are at least one minute (60 seconds) old |
| ./memleak -s 5 |
| Trace roughly every 5th allocation, to reduce overhead |
