Jumbo has a configurable limit of max chunk size (currently 200) but since the splitting is done before headers are filtered out, the chunks are sometimes much smaller than expected.
For instance, third_party/WebKit/Source/core/html lists 610 files in sources which became 4 chunks of ~150 files, but after header filtering that was down to 4 chunks of ~75 files each. Since only 300 of the listed files were cc source files, it should have been 2 chunks of ~150 each.
It would be reasonable to change this and at the same time lower the default chunk size to 100 to get similar results as before.
Comment 1 by bugdroid1@chromium.org
, Jul 26 2017