On Tue, Jul 04, 2023 at 03:20:35PM +0100, Ryan Roberts wrote: > On 04/07/2023 04:45, Yin, Fengwei wrote: > > > > On 7/3/2023 9:53 PM, Ryan Roberts wrote: > >> Introduce FLEXIBLE_THP feature, which allows anonymous memory to be > > THP is for huge page which is 2M size. We are not huge page here. But > > I don't have good name either. > > Is that really true? On arm64 with 16K pages, huge pages are 32M and with 64K > base page, they are 512M. So huge pages already have a variable size. And they > sometimes get PTE-mapped. So can't we just think of this as an extension of the > THP feature? The confusing thing is that we have counters for the number of THP allocated (and number of THP mapped), and for those we always use PMD-size folios. If we must have a config option, then this is ANON_LARGE_FOLIOS. But why do we need a config option? We don't have one for the page cache, and we're better off for it. Yes, it depends on CONFIG_TRANSPARENT_HUGEPAGE today, but that's more of an accidental heritage, and it'd be great to do away with that dependency eventually. Hardware support isn't needed. Large folios benefit us from a software point of view. if we need a chicken bit, we can edit the source code to not create anon folios larger than order 0.
