Is it possible to apply cgroup memory subsystem controls to threads created with
pthread_create() / clone or only tasks that have been created using
fork and exec?
In testing, we seem to be seeing that all allocations are accounted
for against the
PPID / TGID and never the pthread_create()'d TID, even though the TID is an LWP
and can be seen using top (though RSS is aggregate and global of course).
Attached is a simple test program used to print PID / TID and allocate memory
from a cloned TID. After setting breakpoints in child and parent and
setting up a
cgroups hierarchy of 'parent' and 'child', apply memory.limit_in_bytes and
memory.memsw.limit_in_bytes to the child cgroup only and adding the PID to
the parent group and the TID to the child group we see that behaviour.
Is that expected? I realise that the subsystems are all different but
what is confusing
us slightly is that we have previously used the CPU subsystem to set cpu_shares
and adding LWP / TID's to individual cgroups worked just fine for that
Am I misconfiguring somehow or is this a known difference between CPU and
MEMORY subsystems?
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <sys/syscall.h>
void thread_func()
{
printf( "thread pid=%d, thread tid=%d\n", getpid(), syscall( SYS_gettid ) );
size_t one_hundred_mb = 100 * 1024 * 1024;
void * allocatedChunk = malloc ( one_hundred_mb );
memset( allocatedChunk, 0, one_hundred_mb );
if ( allocatedChunk == NULL )
{
printf("couldn't allocate\n");
}
else
{
int tid = syscall( SYS_gettid );
printf( "PID: %d, TID: %d - has allocated 100mb\n", getpid(), syscall( SYS_gettid ) );
}
sleep(1000);
}
void main()
{
printf( "main pid=%d, main tid=%d\n", getpid(), syscall( SYS_gettid ) );
pthread_t thread1;
pthread_create( &thread1, NULL, (void *)&thread_func, NULL);
/* pid_t childpid;
childpid = fork();
if ( childpid >= 0 )
{
if ( childpid == 0 )
{
thread_func(); // child
}
else
{
sleep(1000); // parent
}
}
else
{
perror("fork");
exit(0);
} */
sleep(1000);
}
