On Sun, May 29, 2022 at 04:31:07AM +0100, Matthew Wilcox wrote: > On Sun, May 29, 2022 at 10:58:18AM +0800, Muchun Song wrote: > > On Sat, May 28, 2022 at 05:27:11PM +0100, Matthew Wilcox wrote: > > > On Sun, May 29, 2022 at 12:11:58AM +0800, bh1scw@xxxxxxxxx wrote: > > > > From: Fanjun Kong <bh1scw@xxxxxxxxx> > > > > > > > > This patch will use folio allocation functions for allocating pages. > > > > > > That's not actually a good idea. folio_alloc() will do the > > > prep_transhuge_page() step which isn't needed for slab. > > > > You mean folio_alloc() is dedicated for THP allocation? It is a little > > surprise to me. I thought folio_alloc() is just a variant of alloc_page(), > > which returns a folio struct instead of a page. Seems like I was wrong. > > May I ask what made us decide to do this? > > Yeah, the naming isn't great here. The problem didn't really occur > to me until I saw this patch, and I don't have a good solution yet. OK, I have an idea. None of the sl*b allocators use the page refcount. So the atomic operations on it are just a waste of time. If we add an alloc_unref_page() to match our free_unref_page(), that'll be enough difference to stop pepole sending "helpful" patches. Also, it'll be a (small?) performance improvement for slab.
