I am currently working on a pipeline which loads and transforms multiple images at once. As this is happening to many images at the same time (1440) the memory footprint is quite heavy. I therefore tried to implement a memory management system based on setrlimit, however it doesn't seem to affect the spawned threads (std::thread) as they will happily ignore the limit - I know this because of calls to getrlimit() in the threaded functions - and eventually cause my program to be killed. Here is the code I use for setting the limit:
void setMemoryLimit(std::uint64_t bytes)
{
struct rlimit limit;
getrlimit(RLIMIT_AS, &limit);
if(bytes <= limit.rlim_max)
{
limit.rlim_cur = bytes;
std::cout << "New memory limit: " << limit.rlim_cur << " bytes" << std::endl;
}
else
{
limit.rlim_cur = limit.rlim_max;
std::cout << "WARNING: Memory limit couldn't be set to " << bytes << " bytes" << std::endl;
std::cout << "New memory limit: " << limit.rlim_cur << " bytes" << std::endl;
}
if(setrlimit(RLIMIT_AS, &limit) != 0)
std::perror("WARNING: memory limit couldn't be set:");
// included for debugging purposes
struct rlimit tmp;
getrlimit(RLIMIT_AS, &tmp);
std::cout << "Tmp limit: " << tmp.rlim_cur << " bytes" << std::endl; // prints the correct limit
}
I'm using Linux. The man page states that setrlimit affects the whole process so I'm kind of clueless why the threads don't seem to be affected.
Edit: By the way, the function above is called at the very beginning of main().
The problem was quite hard to find as it consisted of two entirely independent components:
My executable was compiled with -fomit-frame-pointer. This will result in a reset of the limit. See the following example:
/* rlimit.cpp */ #include <iostream> #include <thread> #include <vector> #include <sys/resource.h> class A { public: void foo() { struct rlimit limit; getrlimit(RLIMIT_AS, &limit); std::cout << "Limit: " << limit.rlim_cur << std::endl; } }; int main() { struct rlimit limit; limit.rlim_cur = 500 * 1024 * 1024; setrlimit(RLIMIT_AS, &limit); std::cout << "Limit: " << limit.rlim_cur << std::endl; std::vector<std::thread> t; for(int i = 0; i < 5; i++) { A a; t.push_back(std::thread(&A::foo, &a)); } for(auto thread : t) thread.join(); return 0; }
Outputs:
> g++ -std=c++11 -pthread -fomit-frame-pointer rlimit.cpp -o limit > ./limit Limit: 524288000 Limit: 18446744073709551615 Limit: 18446744073709551615 Limit: 18446744073709551615 Limit: 18446744073709551615 Limit: 18446744073709551615 > g++ -std=c++11 -pthread rlimit.cpp -o limit > ./limit Limit: 524288000 Limit: 524288000 Limit: 524288000 Limit: 524288000 Limit: 524288000 Limit: 524288000
For the image processing part I work with OpenCL. Apparently NVIDIA's implementation calls setrlimit and pushes the limit to rlim_max.
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