A method of video processing is described. The method includes performing a conversion between a current video block of a video picture of a video and a coded representation of the video according to a buffer allocation rule, wherein the conversion uses an intra block copy (IBC) mode in which a prediction of the current video block is derived based on sample values from a same video slice with the current video block, and wherein the sample values are determined by block vectors, wherein the buffer allocation rule specifies that a virtual buffer allocated for the conversion using the IBC mode is greater than a minimum size of memory for storing a portion of the video picture searched for determining the block vectors.