Comment 0 for bug 1887763

As I reported on
  https://lists.gnu.org/archive/html/qemu-devel/2020-07/msg05001.html

TL;DR:
common Host size in CI's is 1-2G - for example Ubuntu Autopkgtests 1.5G
Some of them run Guests of 0.5-1G size in TCG mode (as they often can't rely on having KVM available).

Due to https://git.qemu.org/?p=qemu.git;a=commit;h=600e17b261555c56a048781b8dd5ba3985650013 in qmeu 5.0 the TB default size bumped from 32M to 1G.

The 1G TB buffer + 0.5G actual guest size + there is no dynamic downsizing on memory pressure (never was) makes these systems go OOM-Killing the qemu process.

Let us try to tune back the default size a bit again while the upstream discussion is ongoing.