On Thu, Apr 08, 2021 at 10:49:02AM +0530, Anshuman Khandual wrote: > Adding James here. > > + James Morse <james.morse@xxxxxxx> > > On 4/7/21 10:56 PM, Mike Rapoport wrote: > > From: Mike Rapoport <rppt@xxxxxxxxxxxxx> > > > > Hi, > > > > These patches aim to remove CONFIG_HOLES_IN_ZONE and essentially hardwire > > pfn_valid_within() to 1. > > That would be really great for arm64 platform as it will save CPU cycles on > many generic MM paths, given that our pfn_valid() has been expensive. > > > > > The idea is to mark NOMAP pages as reserved in the memory map and restore > > Though I am not really sure, would that possibly be problematic for UEFI/EFI > use cases as it might have just treated them as normal struct pages till now. I don't think there should be a problem because now the struct pages for UEFI/ACPI never got to be used by the core mm. They were (rightfully) skipped by memblock_free_all() from one side and pfn_valid() and pfn_valid_within() return false for them in various pfn walkers from the other side. > > the intended semantics of pfn_valid() to designate availability of struct > > page for a pfn. > > Right, that would be better as the current semantics is not ideal. > > > > > With this the core mm will be able to cope with the fact that it cannot use > > NOMAP pages and the holes created by NOMAP ranges within MAX_ORDER blocks > > will be treated correctly even without the need for pfn_valid_within. > > > > The patches are only boot tested on qemu-system-aarch64 so I'd really > > appreciate memory stress tests on real hardware. > > Did some preliminary memory stress tests on a guest with portions of memory > marked as MEMBLOCK_NOMAP and did not find any obvious problem. But this might > require some testing on real UEFI environment with firmware using MEMBLOCK_NOMAP > memory to make sure that changing these struct pages to PageReserved() is safe. I surely have no access for such machines :) > > If this actually works we'll be one step closer to drop custom pfn_valid() > > on arm64 altogether. > > Right, planning to rework and respin the RFC originally sent last month. > > https://patchwork.kernel.org/project/linux-mm/patch/1615174073-10520-1-git-send-email-anshuman.khandual@xxxxxxx/ -- Sincerely yours, Mike.
