Re: [RFC PATCH v3 5/5] mm: support large folios swapin as a whole
From: Shakeel Butt <shakeel.butt@linux.dev>
Date: 2024-06-10 20:43:20
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On Thu, Mar 14, 2024 at 08:56:17PM GMT, Chuanhua Han wrote: [...]
quoted
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? _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel