If there's enough for the compressed record, alignment overhead, and a line index entry, it's got a winner. However, the space may not be contiguous. In that case, DPM shuffles all the data down to the bottom of the page. Obviously, it doesn't compress the line index entries, though it does correct the offset for data that has moved. Next step is to create a new line index entry and shoot the data onto the page.
Final step is to see if the page's fullness quotient has changed and make appropriate changes if so.
If there is space on page, but not enough for the current compressed record, DPM marches on through the pointer page, checking plausible candidates, then on through other pointer pages until there are no more allocated data pages. OK, now it's time to allocate a new data page. Next, create the page in a buffer. Now, starting with the first pointer page that has space to hold a new data page pointer, or create a new pointer page for the table. At least that's all I can explain at the moment.