On Fri, 2020-12-04 at 18:12 +1000, Nicholas Piggin wrote: > Excerpts from Edgecombe, Rick P's message of December 1, 2020 6:21 > am: > > On Sun, 2020-11-29 at 01:25 +1000, Nicholas Piggin wrote: > > > Support huge page vmalloc mappings. Config option > > > HAVE_ARCH_HUGE_VMALLOC > > > enables support on architectures that define HAVE_ARCH_HUGE_VMAP > > > and > > > supports PMD sized vmap mappings. > > > > > > vmalloc will attempt to allocate PMD-sized pages if allocating > > > PMD > > > size > > > or larger, and fall back to small pages if that was unsuccessful. > > > > > > Allocations that do not use PAGE_KERNEL prot are not permitted to > > > use > > > huge pages, because not all callers expect this (e.g., module > > > allocations vs strict module rwx). > > > > Several architectures (x86, arm64, others?) allocate modules > > initially > > with PAGE_KERNEL and so I think this test will not exclude module > > allocations in those cases. > > Ah, thanks. I guess archs must additionally ensure that their > PAGE_KERNEL allocations are suitable for huge page mappings before > enabling the option. > > If there is interest from those archs to support this, I have an > early (un-posted) patch that adds an explicit VM_HUGE flag that could > override the pessemistic arch default. It's not much trouble to add > this > to the large system hash allocations. It's very out of date now but > I > can at least give what I have to anyone doing an arch support that > wants it. Ahh, sorry, I totally missed that this was only enabled for powerpc. That patch might be useful for me actually. Or maybe a VM_NOHUGE, since there are only a few places where executable vmallocs are created? I'm not sure what the other issues are. I am endeavoring to have small module allocations share large pages, so this infrastructure is a big help already. https://lore.kernel.org/lkml/20201120202426.18009-1-rick.p.edgecombe@xxxxxxxxx/ Thanks!
