On Fri, Nov 24, 2023 at 06:34:10PM +0100, David Hildenbrand wrote: > On 24.11.23 16:53, Matthew Wilcox wrote: > > > * we already have PMD-sized "large anon folios" in THP > > > > Right, those are already accounted as THP, and that's what users expect. > > If we're allocating 1024 x 64kB chunks of memory, the user won't be able > > to distinguish that from 32 x 2MB chunks of memory, and yet the > > performance profile for some applications will be very different. > > Very right, and because there will be a difference between 1024 x 64kB, 2048 > x 32 kB and so forth, we need new memory stats either way. > > Ryan had some ideas on that, but currently, that's considered future work, > just like it likely is for the pagecache as well and needs much more > thoughts. > > Initially, the admin will have to enable all that for anon either way. It > all boils down to one memory statistic for anon memory (AnonHugePages) > that's messed-up already. So we have FileHugePages which is very carefully only PMD-sized large folios. If people start making AnonHugePages count non-PMD-sized large folios, that's going to be inconsistent. > > am objecting to the use of the term "small THP" on the grounds of > > confusion and linguistic nonsense. > > Maybe that's the reason why FreeBSD calls them "medium-sized superpages", > because "Medium-sized" seems to be more appropriate to express something "in > between". I don't mind "medium" in the name. > So far I thought the reason was because they focused on 64k only. > > Never trust a German guy on naming suggestions. John has so far been my > naming expert, so I'm hoping he can help. > > "Sub-pmd-sized THP" is just mouthful. But then, again, this is would just be > a temporary name, and in the future THP will just naturally come in multiple > sizes (and others here seem to agree on that). I do not. If we'd come to this fifteen years ago, maybe, but people now have an understanding that THPs are necessarily PMD sized.
