On 17/07/2023 16:30, Matthew Wilcox wrote: > On Mon, Jul 17, 2023 at 03:31:08PM +0100, Ryan Roberts wrote: >> In preparation for the introduction of large folios for anonymous >> memory, we would like to be able to split them when they have unmapped >> subpages, in order to free those unused pages under memory pressure. So >> remove the artificial requirement that the large folio needed to be at >> least PMD-sized. >> >> Signed-off-by: Ryan Roberts <ryan.roberts@xxxxxxx> >> Reviewed-by: Yu Zhao <yuzhao@xxxxxxxxxx> >> Reviewed-by: Yin Fengwei <fengwei.yin@xxxxxxxxx> > > Reviewed-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> Thanks! > >> */ >> - if (folio_test_pmd_mappable(folio) && folio_test_anon(folio)) >> + if (folio_test_large(folio) && folio_test_anon(folio)) >> if (!compound || nr < nr_pmdmapped) >> deferred_split_folio(folio); > > I wonder if it's worth introducing a folio_test_deferred_split() (better > naming appreciated ...) to allow us to allocate order-1 folios and not > do horrible things. Maybe it's not worth supporting order-1 folios; > we're always better off going to order-2 immediately. Just thinking. There is more than just _deferred_list in the 3rd page; you also have _flags_2a and _head_2a. I guess you know much better than me what they store. But I'm guessing its harder than jsut not splitting an order-1 page? With the direction of large anon folios (_not_ retrying with every order down to 0), I'm not sure what the use case would be for order-1 anyway?
