Reverting the above commit against mesa git master did not solve the problem.
Performed another bisection and got result:

commit b419c651fbbf3660d7b53623dfa2e5a4c9bd3b98
Author: Marek Olšák <marek.olsak@amd.com>
Date:   Wed Aug 20 23:53:40 2014 +0200

    gallium/pb_bufmgr_cache: limit the size of cache

    This should make a machine which is running piglit more responsive at
times.
    e.g. streaming-texture-leak can easily eat 600 MB because of how fast it
    creates new textures.

Reverting this commit (to remove the cache limit) returned the game to full
performance. Tested against git-ff1948a.