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I plan on discussing possible other soluti= ons >>> at the talk. >> >> Here's an argument. The one remaining caller of add_to_page_cache_lru= () >> is ramfs_nommu_expand_for_mapping(). Attached is a patch which >> eliminates it ... but it doesn't compile because folio_split() is >> undefined on nommu. >> >> So either we need to reimplement all the good stuff that folio_split()= >> does for us, or we need to make folio_split() available on nommu. >> > > I had a question, one conclusion I came to was: folio splitting depends= on THP, so we either need to implement the split logic without THP depen= dency or just make sure we don't split a large folio at all when we use l= arge folio (what I did in this RFC but not a great long term solution). Why? What folio split does: 1. unmap pagecache folios or freeze anon folios with migration entries 2. split the folio to small ones and handle other related meta data like page owner, pgalloc tags, swap, pagecache index info, or others 3. remove migration entries for anon folios, do nothing for pagecache fol= io. Unless the large folio is PMD mapped, splitting other large folios should= work without THP. > > So even if we implement folio_split without any dependency on THP, do w= e need to re-implement or make folio_split available for nommu? I am also= wondering how nommu code is related to removing large folios dependency = on THP. > > -- > Pankaj Best Regards, Yan, Zi