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Re: xmalloc crash

From: Bob Proulx
Subject: Re: xmalloc crash
Date: Sat, 6 Jan 2018 21:13:17 -0700
User-agent: Mutt/1.9.2 (2017-12-15)

Eduardo A. Bustamante López wrote:
> Alfred Baroti wrote:
> > Hi,
> > I found this from long long time ago.
> > Is this a serious bug?
> [...]
> This is not a serious bug at all. It's just a memory allocation failure.

Agreed.  Not a bug at all.

> You can see that the brk() system call actually succeeds.

If you are running under the Linux kernel in the default configuration
then memory overcommit is enabled.

  $ sysctl vm.overcommit_memory

With overcommit enabled brk(), and malloc(), will always succeed even
if there isn't really enough memory.  Neither will fork().  It doesn't
mean there actually is that much memory available.  Later if the
kernel runs out of memory to implement the needs then it will fail and
trigger the OOM Out Of Memory Killer to virtually kill -9 processes
until enough memory is freed up to balance the books.  Processes
killed by the OOM have no opportunity to clean up or log anything.

Or vm.overcommit_memory can be configured the traditional Unix way
where enough virtual memory needs to exist or malloc() and fork() will
fail.  IMNHO overcommit off is the best way for enterprise servers.
However overcommit on is convenient for laptops.


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