Date: Fri, 27 Nov 2009 13:17:31 -0800 From: Maxim Sobolev <sobomax@sippysoft.com> To: "current@freebsd.org" <current@FreeBSD.ORG> Cc: FreeBSD Hackers <freebsd-hackers@FreeBSD.ORG>, stable@FreeBSD.ORG Subject: heap limits: mmap(2) vs. break(2) on i386 Message-ID: <4B1041EB.9020109@sippysoft.com>
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Hi,
I am trying to figure out why java fails to start with 1024MB of heap on
i386 with 4GB of RAM and 4GB of swap. Both MAXDSIZ and DFLDSIZ are set
to 2GB. Here is my limits:
Resource limits (current):
cputime infinity secs
filesize infinity kB
datasize 2097152 kB
stacksize 65536 kB
coredumpsize infinity kB
memoryuse infinity kB
memorylocked infinity kB
maxprocesses 5547
openfiles 20000
sbsize infinity bytes
vmemoryuse infinity kB
Running ktrace I see:
9154 java CALL
mmap(0,0x44000000,PROT_READ|PROT_WRITE|PROT_EXEC,MAP_PRIVATE|MAP_NORESERVE|MAP_ANON,0xffffffff,0,0)
9154 java RET mmap -1 errno 12 Cannot allocate memory
9154 java CALL write(0x1,0xbf9fe378,0x2b)
9154 java GIO fd 1 wrote 43 bytes
"Error occurred during initialization of VM
I made a small program that uses malloc(3) to allocate the same amount
of memory, and that works nicely, ktrace reveals why:
10108 a.out CALL
mmap(0,0x44000000,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANON,0xffffffff,0,0)
10108 a.out RET mmap -1 errno 12 Cannot allocate memory
10108 a.out CALL break(0x4c100000)
10108 a.out RET break 0
So the question is: why does mmap() fails while essentially the same
sbrk() request succeeds? This is really bad since, while native FreeBSD
programs can work around this by using malloc(3), Linux programs and
software that knows nothing about intricate details of the FreeBSD VM
(i.e. Java) will fail miserably.
I tried increasing vm.max_proc_mmap to 2147483647 from default 49344,
but it did not do any good. mmap() still fails with the request of this
size.
I have seen several threads on the issue over the years, but still no
resolution. It seems that only plausible solution is to limit heap size
in java, which may not work for all cases.
Funny thing is that the first sentence of the sbrk(2) manual page says:
The brk() and sbrk() functions are legacy interfaces from before
the advent of modern virtual memory management.
Yet, "legacy interfaces" seems to do much better job than "modern
virtual memory management interfaces"!
-Maxim
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