I have a c++ service, where I am trying to debug the cause of high service startup time. From strace logs I notice a lot of brk() (which contributes to about 300ms, which is very high for our SLA). On studying further , I see brk() to be a memory management call which helps control amount of memory allocated to data segment of the process. malloc() can use brk() (for small allocations) or mmap (for big allocations) based on situation.
Logs from strace:
891905 1674977609.119549 mmap2(NULL, 163840, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xf6a01000 <0.000051>
891905 1674977609.119963 brk(0x209be000) = 0x209be000 <0.000025>
891905 1674977609.120495 brk(0x209df000) = 0x209df000 <0.000022>
891905 1674977609.121167 brk(0x20a00000) = 0x20a00000 <0.000041>
891905 1674977609.121776 brk(0x20a21000) = 0x20a21000 <0.000024>
891905 1674977609.122327 brk(0x20a42000) = 0x20a42000 <0.000024>
...
..
.
891905 1674977609.427039 brk(0x2432b000) = 0x2432b000 <0.000064>
891905 1674977609.427827 brk(0x2434c000) = 0x2434c000 <0.000069>
891905 1674977609.428695 brk(0x2436d000) = 0x2436d000 <0.000050> 0 0 2 2
I believe , there is way number of brk() calls called, which has a scope for improving efficiency . I am trying play around with tunables such as M_TRIM_THRESHOLD, M_MMAP_THRESHOLD to reduce the number of brk() , but I don't notice any change.
https://www.linuxjournal.com/files/linuxjournal.com/linuxjournal/articles/063/6390/6390s2.html
For instance , this is one of the ways I tried to make the changes before restarting the service. The service is running as a docker container, so I am trying to make the changes on the docker container and on the host. , but I don't notice any change.
export MALLOC_MMAP_THRESHOLD_=131072
export MALLOC_TRIM_THRESHOLD_=131072
export MALLOC_MMAP_MAX_=65536
Am I trying to hit the wrong target , or is my understanding there is lot of fragmentation that is happening is wrong. Any help is appreciated.
Thanks