jemalloc enhancement for small-memory systems

[Eike Dierks]

Hi Ian,

I'm trying to understand the underlying problem.
Looks like you already investigated that.
Please tell us more about that.

As far as I understand, jemalloc is not that bad at all.
but it seems to get into conflict with the use of mlockall in some situations.

We should get Jason Evans in the boat
to sort this out.

malloc is not an easy task ...

I once had the idea that the VM in FreeBSD was somehow build upon the Mach VM?
Is this still true today?

How do they cope with this kind of problems in Darwin

~eike















On Dec 22, 2012, at 20:28 , Ian Lepore wrote:

> When a daemon such as watchdogd uses mlockall(2) on a small-memory
> embedded system, it can end up wiring much of the available ram because
> jemalloc allocates large chunks of vmspace by default.  More background
> info on this can be found in this thread:
> 
> http://lists.freebsd.org/pipermail/freebsd-embedded/2012-November/001679.html
> 
> It's hard to tune jemalloc's allocation behavior for this in a
> machine-independent way because the minimum chunk size depends on
> PAGE_SIZE and other factors internal to jemalloc.  I've created a patch
> that addresses this by defining that lg_chunk:0 is implicitly a request
> to set the chunk size to the smallest value allowable for the machine
> it's running on.  The patch is attached to this PR...
> 
> http://www.freebsd.org/cgi/query-pr.cgi?pr=174641
> 
> Jason, could you please review this and consider incorporating it into
> jemalloc?  Or let us know if there's a better way to handle this
> situation.
> 
> -- Ian
> 
> 
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