Dirty pages of cached user data are persistently stored to page buffers that are allocated from a page buffer pool in a persistent data storage resource of a data storage system, and are indicated by page descriptors that are stored at a head of a temporally ordered page descriptor ring as the dirty pages are stored to the page buffers. The disclosed technology performs a flush operation by selecting a work-set of non-sequential page descriptors within the page descriptor ring, flushing dirty pages from page buffers indicated by the page descriptors in the work-set to non-volatile data storage drives of the data storage system, and storing, for each one of the page buffers indicated by the page descriptors in the work-set, an indication that the page buffer is available for re-use.