I've been able to reproduce this with a modified program from the examples
to show the memory consumption I'm seeing. I'm using jemalloc to capture
memory consumption and here's what it looks like for the program below when
repeatedly hitting the endpoint:
allocated: 120072, active: 163840, resident: 9150464
allocated: 150536, active: 196608, resident: 9228288
allocated: 181000, active: 229376, resident: 9306112
allocated: 211464, active: 262144, resident: 9383936
allocated: 211464, active: 262144, resident: 9383936
allocated: 241928, active: 294912, resident: 9461760
allocated: 272392, active: 327680, resident: 9539584
allocated: 272392, active: 327680, resident: 9539584
allocated: 302856, active: 360448, resident: 9617408
The delay in the handler and the use of ASAN tend to inflate the memory
growth. The key factor here seems to be the use of the thread poll with
either poll or epoll. Without the thread pool, there is no memory growth
at all. The growth happens on low connection rates (manual refreshing in
the browser). I haven't yet tried compiling MHD with ASAN.
I'm also not getting responses to my threads in email for some reason but
I'm checking the archive.
#include <cstring>
#include <iostream>
#include <jemalloc/jemalloc.h>
#include <microhttpd.h>
#include <sstream>
#include <thread>
static enum MHD_Result handler(void *, struct MHD_Connection *connection,
const char *url, const char *method,
const char *, const char *, size_t *,
void **ptr) {
static int aptr;
if (&aptr != *ptr) {
*ptr = &aptr;
return MHD_YES;
}
*ptr = NULL;
std::this_thread::sleep_for(std::chrono::milliseconds(40));
size_t sz = sizeof(size_t);
uint64_t epoch = 1;
mallctl("thread.tcache.flush", NULL, NULL, NULL, 0);
mallctl("epoch", &epoch, &sz, &epoch, sz);
std::size_t allocated, active, metadata, resident, mapped;
mallctl("stats.allocated", &allocated, &sz, NULL, 0);
mallctl("stats.active", &active, &sz, NULL, 0);
mallctl("stats.resident", &resident, &sz, NULL, 0);
std::stringstream s;
s << "allocated: " << allocated << ", active: " << active
<< ", resident: " << resident << "\n";
auto msg = s.str();
std::cout << msg;
struct MHD_Response *response = MHD_create_response_from_buffer(
msg.size(), msg.data(), MHD_RESPMEM_MUST_COPY);
MHD_Result ret = MHD_queue_response(connection, MHD_HTTP_OK, response);
MHD_destroy_response(response);
return ret;
}
int main(int argc, char *argv[]) {
struct MHD_Daemon *d;
int port = argc > 1 ? atoi(argv[1]) : 10000;
// epoll mode with thread pool
unsigned int concurrency = std::thread::hardware_concurrency();
std::cout << "concurrency: " << concurrency << "\n";
d = MHD_start_daemon(MHD_USE_EPOLL_INTERNAL_THREAD | MHD_USE_ERROR_LOG,
port,
NULL, NULL, handler, NULL,
MHD_OPTION_CONNECTION_TIMEOUT,
(unsigned int)120, MHD_OPTION_STRICT_FOR_CLIENT,
(int)1,
MHD_OPTION_THREAD_POOL_SIZE, concurrency, NULL,
MHD_OPTION_END);
if (d == NULL)
return 1;
std::cout << "listening on port: " << port << "\n";
std::cout << "hit key to stop"
<< "\n";
// type a key to end
(void)getc(stdin);
MHD_stop_daemon(d);
return 0;
}
Hi Erik,
> Which MHD version are you using?
> Some problems with externally added connections with epoll mode were fixed
> in v0.9.72.
> If you have any blocking calls, make sure that you use connection
> suspend/resume.
> Alternatively, you can you use thread-per-connection mode, this is less
> efficient, but simpler to implement.
> epoll mode does not have special memory allocation, connections are processed
> in the same way, like in other modes. MHD typically does not allocate
> memory during connection processing, except when new connection is
> started.
> Do you use postprosessor or authentication functions? MHD has some memory
> allocs in these functions.
> The issue is not connected with quoted comment definitely. It is just a bad
> wording. Actually nothing is leaked, but may be locked until end of sending
> of response. Moreover, MHD does not use memory pool in the way where such
> lock is possible. Memory pool is reset after each request-reply cycle.
> Memory pool size for each connection is fixed and cannot grow.
> A few suggestions:
> * make sure that you are using the latest MHD version (0.9.73 at the
> moment), * check whether you destroy responses and free all resources
> connected to responses, * if you are testing your code with ASAN, make
> sure that leak detector is enabled. You can build static MHD lib with
> ASAN and link it with our application compiled with ASAN,
> * use Valgrind or simpler tools like memstat or memprof.
> --
> Wishes,
> Evgeny
> On 22.11.2021 22:56, Erik Smith wrote:
> /* Reallocate a block of memory obtained from the pool.
> * This is particularly efficient when growing or
> * shrinking the block that was last (re)allocated.
> * If the given block is not the most recently
> * (re)allocated block, the memory of the previous
> * allocation may be leaked until the pool is
> * destroyed or reset. */
> Can anyone confirm whether this might be related?
> ASAN does not seem to detect any issues in our code presently (not sure about
> MHD)
We have started to experiment with running MHD with epoll + thread pool as
we do the FD limit in certain situations. We understand that there are
caveats to this given that we have some blocking database calls. This seems
to get us past the FD limit errors and the performance is similar.
However, we are running into growing memory consumption in our server over
time running epoll+threads that require a restart frequently. This does
not seem to occur with just epoll (without the thread pool). We are
running jemalloc, but it does not seem to be related to the leak when it is
disabled. There is the following comment in the MHD code for the
MHD_pool_reallocate function that might be connected to this issue:
