We know the ReRAM based on the mechanism of conductive filament has the forming process which need a high voltage to induce.
For some ReRAM based on Mott transition, such as PCMO (Sci. Rep. 2013. 3. 1704; Nanoscale, 2015, 7, 6444–6450) and LSMO (Journal of the Ceramic Society of Japan 122 [8] 622-625 2014), they don't have the forming process.