On Nov 6, 2015, at 2:01 PM, Evan Jones <[email protected]> wrote:
> On Fri, Nov 6, 2015 at 4:57 PM, Jason Evans <[email protected]
> <mailto:[email protected]>> wrote:
> On Nov 6, 2015, at 12:53 PM, Evan Jones <[email protected]
> <mailto:[email protected]>> wrote:
>> On Fri, Nov 6, 2015 at 3:45 PM, Jason Evans <[email protected]
>> <mailto:[email protected]>> wrote:
>> No, dumps are always based on the most recent stats reset (process start or
>> "prof.reset" mallctl call). You can view incremental differences between
>> two dumps by using the --base option to jeprof.
>>
>> Is this true if you use opt.lg_prof_interval? Then what is the point of the
>> opt.prof_accum option?
>
> opt.lg_prof_interval is merely a dump triggering mechanism. opt.prof_accum
> controls whether cumulative stats are collected at all.
>
> There must be something stupid that I don't understand then. You said: "dumps
> are always based on the most recent stats reset", which is usually the
> process start time, unless you do some manual reset. Does this mean that
> prof_accum is *only* useful if you do manually trigger resets using
> mallctl("prof.reset")? Does this mean that with prof_accum:true, the dumps
> contain *both* the data since the last reset *and* the data since profiling
> was enabled?
Take the following function as an example, run with
MALLOC_CONF=prof:true,prof_accum:true :
void g(void *p);
void
f(void) {
unsigned i;
for (i = 0; i < (1U << 20); i++) {
void *p = malloc(1U << 30);
if (i == (1U << 19)) {
mallctl("prof.dump", NULL, NULL, NULL, 0); /* A
*/
mallctl("prof.reset", NULL, NULL, NULL, 0);
mallctl("prof.dump", NULL, NULL, NULL, 0); /* B
*/
}
if (p != NULL) {
g(p);
free(p);
}
}
mallctl("prof.dump", NULL, NULL, NULL, 0); /* C */
}
What will the heap profiling stats (as interpreted by jeprof) dumped at A, B,
and C say regarding the malloc() site in f()?
A:
- Current: ~1 object, ~2^30 bytes
- Cumulative: ~2^19 objects, ~2^49 bytes
B:
- Current: 0 objects, 0 bytes
- Cumulative: 0 objects, 0 bytes
C:
- Current: 0 objects, 0 bytes
- Cumulative: ~2^19 objects, ~2^49 bytes
opt.prof_accum controls whether jemalloc maintains the cumulative stats. With
MALLOC_CONF=prof:true,prof_accum:false, you will get no cumulative stats at
all, no matter when/whether any resets occurred.
Jason_______________________________________________
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