On Sun, Aug 08, 2021 at 09:29:29PM -0700, Hugh Dickins wrote: > 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. It is no longer gated by whether TRANSPARENT_HUGEPAGE is enabled or not. That's a relatively recent change, and I can't say that I've tested it. I'll give it a try today on a PA-RISC system I've booted recently. One of the followup pieces of work that I hope somebody other than myself will undertake is using 64KB PTEs on a 4KB PAGE_SIZE ARM/POWER machine if the stars align.
