RFR(XS): 8193521: glibc wastes memory with default configuration

Andrew Dinn adinn at redhat.com
Fri Dec 15 11:38:19 UTC 2017

On 15/12/17 10:39, Doerr, Martin wrote:
> The VM typically starts more than 20 threads even when only using
> java -version so we mmap several useless GB.

Also, I forgot to mention that it is not mmap calls per se that we need
to worry about but actual /physical commit/ of pages in the mmapped
region. We are not short of mappable address space and we don't incur
any significant cost by mapping the virtual address space we currently use.

I have no doubt your trace is showing a vmem page reservation rather
than a corresponding physical page commit. If the TLS regions mmapped in
your trace were really occupying several GBs of physical pages we would
already have done something about it.


Andrew Dinn
Senior Principal Software Engineer
Red Hat UK Ltd
Registered in England and Wales under Company Registration No. 03798903
Directors: Michael Cunningham, Michael ("Mike") O'Neill, Eric Shander

More information about the hotspot-runtime-dev mailing list