Use Case: Basic Allocator Statistics
Run the ex_stats_print program shown on the Getting Started wiki page:
./ex_stats_printSomething like the following output will result:
___ Begin jemalloc statistics ___
Version: 3.6.0-366-g85ae064e96387347915973dcc1ac15e553259bc9
Assertions disabled
Run-time option settings:
opt.abort: false
opt.lg_chunk: 21
opt.dss: "secondary"
opt.narenas: 16
opt.lg_dirty_mult: 3 (arenas.lg_dirty_mult: 3)
opt.stats_print: false
opt.junk: "false"
opt.quarantine: 0
opt.redzone: false
opt.zero: false
opt.tcache: true
opt.lg_tcache_max: 15
opt.prof: false
opt.prof_prefix: "jeprof"
opt.prof_active: true (prof.active: false)
opt.prof_thread_active_init: true (prof.thread_active_init: false)
opt.lg_prof_sample: 19
opt.prof_accum: false
opt.lg_prof_interval: -1
opt.prof_gdump: false
opt.prof_final: false
opt.prof_leak: false
CPUs: 4
Arenas: 16
Pointer size: 8
Quantum size: 16
Page size: 4096
Min active:dirty page ratio per arena: 8:1
Maximum thread-cached size class: 32768
Chunk size: 2097152 (2^21)
Allocated: 55410400, active: 59056128, metadata: 2861824, resident: 61739008, mapped: 65011712
Current active ceiling: 60817408
arenas[0]:
assigned threads: 1
dss allocation precedence: secondary
min active:dirty page ratio: 8:1
dirty pages: 14418:0 active:dirty, 0 sweeps, 0 madvises, 0 purged
allocated nmalloc ndalloc nrequests
small: 1781472 786 0 96
large: 53628928 858 0 858
huge: 0 0 0 0
total: 55410400 1644 0 954
active: 59056128
mapped: 62914560
metadata: mapped: 1597440, allocated: 180352
bins: size ind allocated nmalloc ndalloc nrequests curregs curruns regs pgs util nfills nflushes newruns reruns
8 0 800 100 0 0 100 1 512 1 0.195 1 0 1 0
---
112 7 11200 100 0 0 100 1 256 7 0.390 1 0 1 0
128 8 256 2 0 2 2 1 32 1 0.062 0 0 1 0
---
224 11 22400 100 0 0 100 1 128 7 0.781 1 0 1 0
---
320 13 20480 64 0 0 64 1 64 5 1 1 0 1 0
---
448 15 28672 64 0 0 64 1 64 7 1 1 0 1 0
512 16 5120 10 0 0 10 2 8 1 0.625 1 0 2 0
640 17 20480 32 0 0 32 1 32 5 1 1 0 1 0
768 18 12288 16 0 0 16 1 16 3 1 1 0 1 0
896 19 43904 49 0 17 49 2 32 7 0.765 1 0 2 0
1024 20 10240 10 0 0 10 3 4 1 0.833 1 0 3 0
1280 21 20480 16 0 0 16 1 16 5 1 1 0 1 0
1536 22 15360 10 0 0 10 2 8 3 0.625 1 0 2 0
1792 23 28672 16 0 0 16 1 16 7 1 1 0 1 0
2048 24 20480 10 0 0 10 5 2 1 1 1 0 5 0
2560 25 25600 10 0 0 10 2 8 5 0.625 1 0 2 0
3072 26 30720 10 0 0 10 3 4 3 0.833 1 0 3 0
3584 27 35840 10 0 0 10 2 8 7 0.625 1 0 2 0
4096 28 40960 10 0 0 10 10 1 1 1 1 0 10 0
5120 29 189440 37 0 27 37 10 4 5 0.925 2 0 10 0
6144 30 61440 10 0 0 10 5 2 3 1 1 0 5 0
7168 31 71680 10 0 0 10 3 4 7 0.833 1 0 3 0
8192 32 81920 10 0 0 10 10 1 2 1 1 0 10 0
10240 33 307200 30 0 20 30 15 2 5 1 3 0 15 0
12288 34 245760 20 0 10 20 20 1 3 1 2 0 20 0
14336 35 430080 30 0 20 30 15 2 7 1 3 0 15 0
large: size ind allocated nmalloc ndalloc nrequests curruns
16384 36 327680 20 0 20 20
20480 37 839680 41 0 41 41
24576 38 1007616 41 0 41 41
28672 39 1204224 42 0 42 42
32768 40 1343488 41 0 41 41
40960 41 3358720 82 0 82 82
49152 42 4079616 83 0 83 83
57344 43 4702208 82 0 82 82
65536 44 5373952 82 0 82 82
81920 45 13434880 164 0 164 164
98304 46 16121856 164 0 164 164
114688 47 1835008 16 0 16 16
---
huge: size ind allocated nmalloc ndalloc nrequests curhchunks
---
--- End jemalloc statistics ---
The output is pretty self-explanatory if you have read the jemalloc(3) manual page. Historically, the purpose of such statistics was to aid understanding of what jemalloc is actually doing internally in response to an application's memory allocation activity, in order to improve the allocator. In practice the statistics are also useful to application developers; they give a strong indication of what jemalloc is up to, in terms of system calls, current memory usage, fragmentation, etc. If the allocator is behaving unexpectedly, browse the stats for an obvious cause before resorting to more sophisticated analyses.
Note that by default jemalloc uses thread-local storage for object caching, and the statistics are only merged to the arena statistics counters whenever the arena has to be locked for some reason besides statistics gathering. Thus these counters tend to be slightly out of date, but the inaccuracies are proportionally very small for non-toy applications that have been running for more than a short time. That said, jemalloc does merge all statistics when the application exits. Run the application as such to cause final statistics to be printed:
MALLOC_CONF=stats_print:true ./ex_stats_printThese statistics are accurate (as long as other threads aren't allocating during application exit).