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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: 3.4.1-10-g96eeaec5dd5ac4d11be36945240fa823abc0c3f9
Assertions disabled
Run-time option settings:
opt.abort: false
opt.lg_chunk: 22
opt.dss: "secondary"
opt.narenas: 128
opt.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
opt.lg_prof_sample: 19
opt.prof_accum: false
opt.lg_prof_interval: -1
opt.prof_gdump: false
opt.prof_final: true
opt.prof_leak: false
CPUs: 32
Arenas: 128
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: 4194304 (2^22)
Allocated: 52919712, active: 52940800, mapped: 62914560
Current active ceiling: 54525952
chunks: nchunks highchunks curchunks
15 15 15
huge: nmalloc ndalloc allocated
0 0 0
arenas[0]:
assigned threads: 1
dss allocation precedence: secondary
dirty pages: 12925:0 active:dirty, 0 sweeps, 0 madvises, 0 purged
allocated nmalloc ndalloc nrequests
small: 1015200 969 0 0
large: 51904512 965 0 965
total: 52919712 1934 0 965
active: 52940800
mapped: 54525952
bins: bin size regs pgs allocated nmalloc ndalloc nrequests nfills nflushes newruns reruns curruns
0 8 501 1 800 100 0 0 1 0 1 0 1
[1..6]
7 112 72 2 8064 72 0 0 1 0 1 0 1
[8..10]
11 224 72 4 16128 72 0 0 1 0 1 0 1
[12]
13 320 63 5 20160 63 0 0 1 0 1 0 1
[14]
15 448 63 7 28224 63 0 0 1 0 1 0 1
16 512 63 8 32256 63 0 0 1 0 1 0 1
17 640 51 8 32640 51 0 0 1 0 1 0 1
18 768 47 9 36096 47 0 0 1 0 1 0 1
19 896 45 10 40320 45 0 0 1 0 1 0 1
20 1024 63 16 64512 63 0 0 1 0 1 0 1
21 1280 51 16 65280 51 0 0 1 0 1 0 1
22 1536 42 16 64512 42 0 0 1 0 1 0 1
23 1792 38 17 68096 38 0 0 1 0 1 0 1
24 2048 65 33 133120 65 0 0 1 0 1 0 1
25 2560 52 33 133120 52 0 0 1 0 1 0 1
26 3072 43 33 132096 43 0 0 1 0 1 0 1
27 3584 39 35 139776 39 0 0 1 0 1 0 1
large: size pages nmalloc ndalloc nrequests curruns
4096 1 5 0 5 5
8192 2 41 0 41 41
12288 3 41 0 41 41
16384 4 41 0 41 41
20480 5 41 0 41 41
24576 6 41 0 41 41
28672 7 41 0 41 41
32768 8 42 0 42 42
36864 9 41 0 41 41
40960 10 41 0 41 41
45056 11 41 0 41 41
49152 12 41 0 41 41
53248 13 41 0 41 41
57344 14 41 0 41 41
61440 15 41 0 41 41
65536 16 41 0 41 41
69632 17 41 0 41 41
73728 18 41 0 41 41
77824 19 41 0 41 41
81920 20 41 0 41 41
86016 21 41 0 41 41
90112 22 41 0 41 41
94208 23 41 0 41 41
98304 24 41 0 41 41
102400 25 16 0 16 16
[991]
--- 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).