On Tue, Jun 11, 2024 at 12:23:41PM GMT, Barry Song wrote: > On Tue, Jun 11, 2024 at 8:43 AM Shakeel Butt <shakeel.butt@xxxxxxxxx> wrote: > > > > 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? > > no need to say sorry. You are always welcome to give comments. > > this, combining with zram modification, not only improves compression > ratio but also reduces CPU time significantly. you may find some data > here[1]. > > granularity orig_data_size compr_data_size time(us) > 4KiB-zstd 1048576000 246876055 50259962 > 64KiB-zstd 1048576000 199763892 18330605 > > On mobile devices, We tested the performance of swapin by running > 100 iterations of swapping in 100MB of data ,and the results were > as follows.the swapin speed increased by about 45%. > > time consumption of swapin(ms) > lz4 4k 45274 > lz4 64k 22942 > > zstdn 4k 85035 > zstdn 64k 46558 Thanks for the response. Above numbers are actually very fascinating and counter intuitive (at least to me). Do you also have numbers for 2MiB THP? I am assuming 64k is the right balance between too small or too large. Did you experiment on server machines as well? > > [1] https://lore.kernel.org/linux-mm/20240327214816.31191-1-21cnbao@xxxxxxxxx/ > > Thanks > Barry
