On Sat, 7 Aug 2021, Matthew Wilcox wrote: > > I am, however, of the opinion that 2MB pages give us so much trouble > because they're so very special. Few people exercise those code paths and > it's easy to break them without noticing. This is partly why I want to > do arbitrary-order pages. If everybody is running with compound pages > all the time, we'll see the corner cases often, and people other than > Hugh, Kirill and Mike will be able to work on them. I don't entirely agree. I'm all for your use of compound pages in page cache, but don't think its problems are representative of the problems in aiming for a PMD (or PUD) bar, with the weird page table transitions we expect of "THP" there. I haven't checked: is your use of compound pages in page cache still limited to the HAVE_ARCH_TRANSPARENT_HUGEPAGE architectures? When the others could just as well use compound pages in page cache too. Hugh
