Barry Song <21cnbao@xxxxxxxxx> writes: > From: Chuanhua Han <hanchuanhua@xxxxxxxx> > > On an embedded system like Android, more than half of anon memory is > actually in swap devices such as zRAM. For example, while an app is > switched to background, its most memory might be swapped-out. > > Now we have mTHP features, unfortunately, if we don't support large folios > swap-in, once those large folios are swapped-out, we immediately lose the > performance gain we can get through large folios and hardware optimization > such as CONT-PTE. > > This patch brings up mTHP swap-in support. Right now, we limit mTHP swap-in > to those contiguous swaps which were likely swapped out from mTHP as a > whole. > > Meanwhile, the current implementation only covers the SWAP_SYCHRONOUS > case. It doesn't support swapin_readahead as large folios yet since this > kind of shared memory is much less than memory mapped by single process. In contrast, I still think that it's better to start with normal swap-in path, then expand to SWAP_SYCHRONOUS case. In normal swap-in path, we can take advantage of swap readahead information to determine the swapped-in large folio order. That is, if the return value of swapin_nr_pages() > 1, then we can try to allocate and swapin a large folio. To do that, we need to track whether the sub-pages are accessed. I guess we need that information for large file folio readahead too. Hi, Matthew, Can you help us on tracking whether the sub-pages of a readahead large folio has been accessed? > Right now, we are re-faulting large folios which are still in swapcache as a > whole, this can effectively decrease extra loops and early-exitings which we > have increased in arch_swap_restore() while supporting MTE restore for folios > rather than page. On the other hand, it can also decrease do_swap_page as > PTEs used to be set one by one even we hit a large folio in swapcache. > -- Best Regards, Huang, Ying
