mjhjmtu

The --vm flag of stress command says that,

-m, --vm N spawn N workers spinning on malloc()/free()

I wanted to see what it is actually doing so I ran this command,

strace stress --vm 1

I get the following output,

execve("/bin/stress", ["stress", "--vm", "1"], [/* 27 vars */]) = 0
brk(NULL) = 0x55f05bef2000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fce9f15a000
access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
fstat(3, st_mode=S_IFREG) = 0
mmap(NULL, 40388, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7fce9f150000
close(3) = 0
open("/lib64/libm.so.6", O_RDONLY|O_CLOEXEC) = 3
read(3, "177ELF21133>1pS"..., 832) = 832
fstat(3, 0755, st_size=1139680, ...) = 0
mmap(NULL, 3150136, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fce9ec38000
mprotect(0x7fce9ed39000, 2093056, PROT_NONE) = 0
mmap(0x7fce9ef38000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x100000) = 0x7fce9ef38000
close(3) = 0
open("/lib64/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
read(3, "177ELF21133>1P%2"..., 832) = 832
fstat(3, st_mode=S_IFREG) = 0
mmap(NULL, 3981792, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fce9e86b000
mprotect(0x7fce9ea2e000, 2093056, PROT_NONE) = 0
mmap(0x7fce9ec2d000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1c2000) = 0x7fce9ec2d000
mmap(0x7fce9ec33000, 16864, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7fce9ec33000
close(3) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fce9f14f000
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fce9f14d000
arch_prctl(ARCH_SET_FS, 0x7fce9f14d740) = 0
mprotect(0x7fce9ec2d000, 16384, PROT_READ) = 0
mprotect(0x7fce9ef38000, 4096, PROT_READ) = 0
mprotect(0x55f05abdb000, 4096, PROT_READ) = 0
mprotect(0x7fce9f15b000, 4096, PROT_READ) = 0
munmap(0x7fce9f150000, 40388) = 0
getpid() = 5305
fstat(1, st_mode=S_IFCHR) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fce9f159000
write(1, "stress: info: [5305] dispatching"..., 64stress: info: [5305] dispatching hogs: 0 cpu, 0 io, 1 vm, 0 hdd
) = 64
clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x7fce9f14da10) = 5306
wait4(-1

The output just stuck here and I don't see any malloc() calls either.
How can I see it making malloc() and free() systemcalls?

malloc and free are library calls not system calls.
this is why they are in section 3 of the manual

mmap and munmap are system calls.

If you haven't already do man 2 intro and man 3 intro