Delphi + Linux + 线程 = 内存

Question

Have a memory problem. Small app (server on few ports, TMS+Indy, Delphi 10.3) is using about 2 Gb of memory (to compare - only 6 Mb under Windows).

So, small test, almost empty console app:

var x: TThread;
begin
    x := TThread.Create(true);

after Create (looking internally - after pthread_create ) "pmap" in Ubuntu says that few memory blocks was added as: 4 kb + 132 kb + 8192 kb + 65404 kb

4 + 132 kb - not too large, ok

8 mb - looks as default stack size for a thread, ok

but what is 64 Mb????

Answer 1

The pmap entry is not the consumed memory, it is the reserved/mapped memory.

RAM is first reserved/mapped, but actually consumed per page (typically 4KB), the first time a page is accessed by the program.

IIRC under Linux, the Delphi memory manager is just a wrapper around the libc malloc free API calls. It is typical for this MM to reserve some per-thread memory pages for the thread-specific memory arena. I guess 64MB is a plausible value.

So don't be afraid about those numbers. They don't imply that your RAM chips are consumed eagerly. You can have a process reserving GB of memory, but actually only using a few 100MB of hardware RAM - the writeable/private value in pmap . And note that a Delphi app will consume typically lower than any GC program. :)

Update/Proposal after comments: If you need to reduce memory, don't use threads, but non-blocking inet libraries, or a thread pool and a reverse proxy (eg nginx) to maintain the inet connections. You can have your server handle HTTP/1.0 in a thread pool, and your nginx proxy maintain HTTP/1.1 or HTTP/2 long standing connections. If you use Posix sockets between nginx and the service on the loopback, it is very efficient. We use this configuration with our mORMot services on high production Linux systems, with great stability.

Update/More Info: This 64MB mapping seems indeed the per-thread-arena reserved mapped memory from malloc. Check https://codearcana.com/posts/2016/07/11/arena-leak-in-glibc.html and MALLOC_ARENA_MAX as detailed in https://siddhesh.in/posts/malloc-per-thread-arenas-in-glibc.html