On Wed, Sep 28, 2016 at 09:19:51AM +0200, Raimo Niskanen wrote:
> Dear misc@
>
> I have searched the archives and read the documentation of login.conf(5),
> ksh(1):ulimit and can not find how to limit the amount of physical memory a
> process may use.
>
> I have the following limits where I have set down ulimit -m and ulimit -l
> to 10000 kbytes in an attempt to limit the process I spawn which is
> the Erlang VM.
>
> $ ulimit -a
> time(cpu-seconds) unlimited
> file(blocks) unlimited
> coredump(blocks) unlimited
> data(kbytes) 33554432
> stack(kbytes) 8192
> lockedmem(kbytes) 10000
> memory(kbytes) 10000
> nofiles(descriptors) 1024
> processes 1024
>
> Note that the machine has got 8 GB of physical memory and 8 GB of swap and
> that I have set datasize=infinity in /etc/login.conf. I got
> datasize=33554432 which seems to be the same as kern.shminfo.shmmax.
> The datasize is twice the physical memory + swap.
>
> Then I start the Erlang VM and tell it to allocate an address block of 30000
> MByte for future use where it will store all literal data in the same block
> (this is a garbage collector optimization). Not much of this data is
> actually used.
>
> 68196 beam CALL
> mmap(0,0x753000000,0<PROT_NONE>,0x1002<MAP_PRIVATE|MAP_ANON>,-1,0)
> 68196 beam RET mmap 11871265173504/0xacbfe8b3000
>
> Note the protection flags on the block. No access is allowed. This trick
> works just fine; here is what top says:
>
> load averages: 0.15, 0.13, 0.09 frerin.otp.ericsson.se 08:49:46
> 48 processes: 47 idle, 1 on processor up 13:49
> CPU0 states: 0.0% user, 0.0% nice, 0.0% system, 0.0% interrupt, 100% idle
> CPU1 states: 0.0% user, 0.0% nice, 0.0% system, 0.0% interrupt, 100% idle
> Memory: Real: 43M/636M act/tot Free: 7028M Cache: 508M Swap: 0K/8155M
>
> PID USERNAME PRI NICE SIZE RES STATE WAIT TIME CPU COMMAND
> 68196 raimo 2 0 29G 15M sleep poll 0:00 1.42% beam
>
> So I have a process with a data size of 29 GB on a machine with 16 GB
> memory + swap. I have also tried to start an additional Erlang VM that
> also allocates 29 GB of virtual memory which also works.
>
> That this is allowed is just fine for me - this trick of allocating a
> "large enough" PROT_NONE memory to get one address range for some special
> data type is very useful for the Erlang VM. But I wonder how to limit the
> actual memory use? Setting down ulimit -m and ulimit -l to 10000 kbytes
> did not prevent this process from getting 15 MByte of "RES" memory...
>
> Is there some way to limit the actual amount of memory for a process when I
> need to set up the datasize to allow for large unused virtual memory
> blocks?
I have found clues in getrlimit,setrlimit(2):
RLIMIT_DATA The maximum size (in bytes) of the data segment for a
process; this includes memory allocated via malloc(3)
and all other anonymous memory mapped via mmap(2).
:
RLIMIT_RSS The maximum size (in bytes) to which a process's
resident set size may grow. This imposes a limit
on the amount of physical memory to be given to a
process; if memory is tight, the system will prefer
to take memory from processes that are exceeding
their declared resident set size.
Now I try to figure out the implications of this... If I set the data size
so the sum of the data sizes for all processes in the system is larger than
physical memory + swap, then any process may allocate the last block of
memory in the system so a more important process later will fail to
allocate?
And the memoryuse limit is rather toothless since there is no immediate
check of this limit. When the system gets low on memory; is all that
happens that processes that exceed their memoryuse limit probably will get
blocks swapped out?
If this is correct then programs that for efficiency reasons allocates
large address ranges of which most is rarely used are hard to control
safely with this resource limit model, or programs that use this behaviour
must be considered ill-behaved whith this resource limit model...
Or have I misunderstood something?
>
> dmesg | head -4:
> OpenBSD 6.0 (GENERIC.MP) #1: Fri Sep 23 08:53:49 CEST 2016
>
> r...@stable-60-amd64.mtier.org:/binpatchng/work-binpatch60-amd64/src/sys/arch/amd64/compile/GENERIC.MP
> real mem = 8283037696 (7899MB)
> avail mem = 8027529216 (7655MB)
>
--
/ Raimo Niskanen, Erlang/OTP, Ericsson AB
