On Thu, Mar 14, 2024 at 08:56:17PM GMT, Chuanhua Han wrote: [...] > > > > So in the common case, swap-in will pull in the same size of folio as was > > swapped-out. Is that definitely the right policy for all folio sizes? Certainly > > it makes sense for "small" large folios (e.g. up to 64K IMHO). But I'm not sure > > it makes sense for 2M THP; As the size increases the chances of actually needing > > all of the folio reduces so chances are we are wasting IO. There are similar > > arguments for CoW, where we currently copy 1 page per fault - it probably makes > > sense to copy the whole folio up to a certain size. > For 2M THP, IO overhead may not necessarily be large? :) > 1.If 2M THP are continuously stored in the swap device, the IO > overhead may not be very large (such as submitting bio with one > bio_vec at a time). > 2.If the process really needs this 2M data, one page-fault may perform > much better than multiple. > 3.For swap devices like zram,using 2M THP might also improve > decompression efficiency. > Sorry for late response, do we have any performance data backing the above claims particularly for zswap/swap-on-zram cases?
