[Maxima-discuss] Large memory allocations on Linux & WSL (Windows Subsystem for Linux)

[Henry B. <hb...@pi...>]

Hi all:

I want to be able to test some extremely large Maxima calculations,
so I've been playing with my computer to see how large a memory
space a program could utilize before it started paging itself to death.

I just ran some tests on my current laptop with 16GB of RAM running
WSL2 (Windows Subsystem for Linux) on top of Windows 11.

My tests involved little more than a "Hello World" C program which also
did a large malloc and then initialized the data.

Actually, I used 'aligned_alloc' instead of 'malloc', but I expect that they
both do roughly the same things.

I was able to allocate a single object up to 2^32 *bytes* long (i.e., 4GB),
and this object initialized properly and quite quickly (i.e., no paging).

However, when I tried 2^33 bytes long (i.e., 8GB), the program works, but it
pages like crazy.  But I have 10GB of RAM free, so there should be plenty
of room for an 8GB object completely in RAM in a trivial program like this.

I checked 'prlimit -l', and both the hard & soft limits seem to allow 131072
pages of 'memlock'ed (non-pageable) memory.

However 'ulimit -l' reports a limit of only 65536 pages of memlock'ed
memory. Even after fiddling with /etc/security/limits.conf, I still couldn't
increase the amount that 'ulimit -l' returns.

I'm currently not running a pure Linux on this machine, so I can't tell if
the problem is Linux (Ubuntu) itself, or whether the problem is WSL.

Any thoughts ?