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Message-ID: <aa4b6c90-6e8c-4943-ba83-6688cdf776a1@oracle.com>
Date: Fri, 18 Oct 2024 15:19:45 -0400
From: Joseph Salisbury <joseph.salisbury@...cle.com>
To: David Hildenbrand <david@...hat.com>, Ryan Roberts
<ryan.roberts@....com>,
Andrew Morton <akpm@...ux-foundation.org>,
Anshuman Khandual <anshuman.khandual@....com>,
Ard Biesheuvel <ardb@...nel.org>,
Catalin Marinas <catalin.marinas@....com>,
Greg Marsden <greg.marsden@...cle.com>,
Ivan Ivanov <ivan.ivanov@...e.com>,
Kalesh Singh <kaleshsingh@...gle.com>, Marc Zyngier <maz@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Matthias Brugger <mbrugger@...e.com>, Miroslav Benes <mbenes@...e.cz>,
Will Deacon <will@...nel.org>
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
linux-mm@...ck.org
Subject: Re: [External] : Re: [RFC PATCH v1 00/57] Boot-time page size
selection for arm64
On 10/18/24 14:27, David Hildenbrand wrote:
> On 18.10.24 20:15, Joseph Salisbury wrote:
>>
>>
>>
>> On 10/14/24 06:55, Ryan Roberts wrote:
>>> Hi All,
>>>
>>> Patch bomb incoming... This covers many subsystems, so I've included
>>> a core set
>>> of people on the full series and additionally included maintainers
>>> on relevant
>>> patches. I haven't included those maintainers on this cover letter
>>> since the
>>> numbers were far too big for it to work. But I've included a link to
>>> this cover
>>> letter on each patch, so they can hopefully find their way here. For
>>> follow up
>>> submissions I'll break it up by subsystem, but for now thought it
>>> was important
>>> to show the full picture.
>>>
>>> This RFC series implements support for boot-time page size selection
>>> within the
>>> arm64 kernel. arm64 supports 3 base page sizes (4K, 16K, 64K), but
>>> to date, page
>>> size has been selected at compile-time, meaning the size is baked
>>> into a given
>>> kernel image. As use of larger-than-4K page sizes become more
>>> prevalent this
>>> starts to present a problem for distributions. Boot-time page size
>>> selection
>>> enables the creation of a single kernel image, which can be told
>>> which page size
>>> to use on the kernel command line.
>>>
>>> Why is having an image-per-page size problematic?
>>> =================================================
>>>
>>> Many traditional distros are now supporting both 4K and 64K. And
>>> this means
>>> managing 2 kernel packages, along with drivers for each. For some,
>>> it means
>>> multiple installer flavours and multiple ISOs. All of this adds up to a
>>> less-than-ideal level of complexity. Additionally, Android now
>>> supports 4K and
>>> 16K kernels. I'm told having to explicitly manage their KABI for
>>> each kernel is
>>> painful, and the extra flash space required for both kernel images
>>> and the
>>> duplicated modules has been problematic. Boot-time page size
>>> selection solves
>>> all of this.
>>>
>>> Additionally, in starting to think about the longer term deployment
>>> story for
>>> D128 page tables, which Arm architecture now supports, a lot of the
>>> same
>>> problems need to be solved, so this work sets us up nicely for that.
>>>
>>> So what's the down side?
>>> ========================
>>>
>>> Well nothing's free; Various static allocations in the kernel image
>>> must be
>>> sized for the worst case (largest supported page size), so image
>>> size is in line
>>> with size of 64K compile-time image. So if you're interested in 4K
>>> or 16K, there
>>> is a slight increase to the image size. But I expect that problem
>>> goes away if
>>> you're compressing the image - its just some extra zeros. At
>>> boot-time, I expect
>>> we could free the unused static storage once we know the page size -
>>> although
>>> that would be a follow up enhancement.
>>>
>>> And then there is performance. Since PAGE_SIZE and friends are no
>>> longer
>>> compile-time constants, we must look up their values and do
>>> arithmetic at
>>> runtime instead of compile-time. My early perf testing suggests this is
>>> inperceptible for real-world workloads, and only has small impact on
>>> microbenchmarks - more on this below.
>>>
>>> Approach
>>> ========
>>>
>>> The basic idea is to rid the source of any assumptions that
>>> PAGE_SIZE and
>>> friends are compile-time constant, but in a way that allows the
>>> compiler to
>>> perform the same optimizations as was previously being done if they
>>> do turn out
>>> to be compile-time constant. Where constants are required, we use
>>> limits;
>>> PAGE_SIZE_MIN and PAGE_SIZE_MAX. See commit log in patch 1 for full
>>> description
>>> of all the classes of problems to solve.
>>>
>>> By default PAGE_SIZE_MIN=PAGE_SIZE_MAX=PAGE_SIZE. But an arch may
>>> opt-in to
>>> boot-time page size selection by defining PAGE_SIZE_MIN &
>>> PAGE_SIZE_MAX. arm64
>>> does this if the user selects the CONFIG_ARM64_BOOT_TIME_PAGE_SIZE
>>> Kconfig,
>>> which is an alternative to selecting a compile-time page size.
>>>
>>> When boot-time page size is active, the arch pgtable geometry macro
>>> definitions
>>> resolve to something that can be configured at boot. The arm64
>>> implementation in
>>> this series mainly uses global, __ro_after_init variables. I've
>>> tried using
>>> alternatives patching, but that performs worse than loading from
>>> memory; I think
>>> due to code size bloat.
>>>
>>> Status
>>> ======
>>>
>>> When CONFIG_ARM64_BOOT_TIME_PAGE_SIZE is selected, I've only
>>> implemented enough
>>> to compile the kernel image itself with defconfig (and a few other
>>> bits and
>>> pieces). This is enough to build a kernel that can boot under QEMU
>>> or FVP. I'll
>>> happily do the rest of the work to enable all the extra drivers, but
>>> wanted to
>>> get feedback on the shape of this effort first. If anyone wants to
>>> do any
>>> testing, and has a must-have config, let me know and I'll prioritize
>>> enabling it
>>> first.
>>>
>>> The series is arranged as follows:
>>>
>>> - patch 1: Add macros required for converting non-arch
>>> code to support
>>> boot-time page size selection
>>> - patches 2-36: Remove PAGE_SIZE compile-time constant
>>> assumption from all
>>> non-arch code
>>> - patches 37-38: Some arm64 tidy ups
>>> - patch 39: Add macros required for converting arm64 code
>>> to support
>>> boot-time page size selection
>>> - patches 40-56: arm64 changes to support boot-time page size
>>> selection
>>> - patch 57: Add arm64 Kconfig option to enable boot-time
>>> page size
>>> selection
>>>
>>> Ideally, I'd like to get the basics merged (something like this
>>> series), then
>>> incrementally improve it over a handful of kernel releases until we can
>>> demonstrate that we have feature parity with the compile-time build
>>> and no
>>> performance blockers. Once at that point, ideally the compile-time
>>> build options
>>> would be removed and the code could be cleaned up further.
>>>
>>> One of the bigger peices that I'd propose to add as a follow up, is
>>> to make
>>> va-size boot-time selectable too. That will greatly simplify LPA2
>>> fallback
>>> handling.
>>>
>>> Assuming people are ammenable to the rough shape, how would I go
>>> about getting
>>> the non-arch changes merged? Since they cover many subsystems, will
>>> each piece
>>> need to go independently to each relevant maintainer or could it all
>>> be merged
>>> together through the arm64 tree?
>>>
>>> Image Size
>>> ==========
>>>
>>> The below shows the size of a defconfig (+ xfs, squashfs, ftrace,
>>> kprobes)
>>> kernel image on disk for base (before any changes applied), compile
>>> (with
>>> changes, configured for compile-time page size) and boot (with changes,
>>> configured for boot-time page size).
>>>
>>> You can see the that compile-16k and 64k configs are actually
>>> slightly smaller
>>> than the baselines; that's due to optimizing some buffer sizes which
>>> didn't need
>>> to depend on page size during the series. The boot-time image is ~1%
>>> bigger than
>>> the 64k compile-time image. I believe there is scope to improve this
>>> to make it
>>> equal to compile-64k if required:
>>>
>>> | config | size/KB | diff/KB | diff/% |
>>> |-------------|---------|---------|---------|
>>> | base-4k | 54895 | 0 | 0.0% |
>>> | base-16k | 55161 | 266 | 0.5% |
>>> | base-64k | 56775 | 1880 | 3.4% |
>>> | compile-4k | 54895 | 0 | 0.0% |
>>> | compile-16k | 55097 | 202 | 0.4% |
>>> | compile-64k | 56391 | 1496 | 2.7% |
>>> | boot-4K | 57045 | 2150 | 3.9% |
>>>
>>> And below shows the size of the image in memory at run-time,
>>> separated for text
>>> and data costs. The boot image has ~1% text cost; most likely due to
>>> the fact
>>> that PAGE_SIZE and friends are not compile-time constants so need
>>> instructions
>>> to load the values and do arithmetic. I believe we could eventually
>>> get the data
>>> cost to match the cost for the compile image for the chosen page
>>> size by freeing
>>> the ends of the static buffers not needed for the selected page size:
>>>
>>> | | text | text | text | data | data |
>>> data |
>>> | config | size/KB | diff/KB | diff/% | size/KB | diff/KB |
>>> diff/% |
>>> |-------------|---------|---------|---------|---------|---------|---------|
>>>
>>> | base-4k | 20561 | 0 | 0.0% | 14314 | 0 | 0.0% |
>>> | base-16k | 20439 | -122 | -0.6% | 14625 | 311 | 2.2% |
>>> | base-64k | 20435 | -126 | -0.6% | 15673 | 1359 |
>>> 9.5% |
>>> | compile-4k | 20565 | 4 | 0.0% | 14315 | 1 | 0.0% |
>>> | compile-16k | 20443 | -118 | -0.6% | 14517 | 204 | 1.4% |
>>> | compile-64k | 20439 | -122 | -0.6% | 15134 | 820 | 5.7% |
>>> | boot-4K | 20811 | 250 | 1.2% | 15287 | 973 | 6.8% |
>>>
>>> Functional Testing
>>> ==================
>>>
>>> I've build-tested defconfig for all arches supported by tuxmake
>>> (which is most)
>>> without issue.
>>>
>>> I've boot-tested arm64 with CONFIG_ARM64_BOOT_TIME_PAGE_SIZE for all
>>> page sizes
>>> and a few va-sizes, and additionally have run all the mm-selftests,
>>> with no
>>> regressions observed vs the equivalent compile-time page size build
>>> (although
>>> the mm-selftests have a few existing failures when run against 16K
>>> and 64K
>>> kernels - those should really be investigated and fixed independently).
>>>
>>> Test coverage is lacking for many of the drivers that I've touched,
>>> but in many
>>> cases, I'm hoping the changes are simple enough that review might
>>> suffice?
>>>
>>> Performance Testing
>>> ===================
>>>
>>> I've run some limited performance benchmarks:
>>>
>>> First, a real-world benchmark that causes a lot of page table
>>> manipulation (and
>>> therefore we would expect to see regression here if we are going to
>>> see it
>>> anywhere); kernel compilation. It barely registers a change. Values
>>> are times,
>>> so smaller is better. All relative to base-4k:
>>>
>>> | | kern | kern | user | user | real |
>>> real |
>>> | config | mean | stdev | mean | stdev | mean |
>>> stdev |
>>> |-------------|---------|---------|---------|---------|---------|---------|
>>>
>>> | base-4k | 0.0% | 1.1% | 0.0% | 0.3% | 0.0% |
>>> 0.3% |
>>> | compile-4k | -0.2% | 1.1% | -0.2% | 0.3% | -0.1% |
>>> 0.3% |
>>> | boot-4k | 0.1% | 1.0% | -0.3% | 0.2% | -0.2% |
>>> 0.2% |
>>>
>>> The Speedometer JavaScript benchmark also shows no change. Values
>>> are runs per
>>> min, so bigger is better. All relative to base-4k:
>>>
>>> | config | mean | stdev |
>>> |-------------|---------|---------|
>>> | base-4k | 0.0% | 0.8% |
>>> | compile-4k | 0.4% | 0.8% |
>>> | boot-4k | 0.0% | 0.9% |
>>>
>>> Finally, I've run some microbenchmarks known to stress page table
>>> manipulations
>>> (originally from David Hildenbrand). The fork test maps/allocs 1G of
>>> anon
>>> memory, then measures the cost of fork(). The munmap test
>>> maps/allocs 1G of anon
>>> memory then measures the cost of munmap()ing it. The fork test is
>>> known to be
>>> extremely sensitive to any changes that cause instructions to be
>>> aligned
>>> differently in cachelines. When using this test for other changes,
>>> I've seen
>>> double digit regressions for the slightest thing, so 12% regression
>>> on this test
>>> is actually fairly good. This likely represents the extreme worst
>>> case for
>>> regressions that will be observed across other microbenchmarks
>>> (famous last
>>> words). Values are times, so smaller is better. All relative to
>>> base-4k:
>>>
>>> | | fork | fork | munmap | munmap |
>>> | config | mean | stdev | stdev | stdev |
>>> |-------------|---------|---------|---------|---------|
>>> | base-4k | 0.0% | 1.3% | 0.0% | 0.3% |
>>> | compile-4k | 0.1% | 1.3% | -0.9% | 0.1% |
>>> | boot-4k | 12.8% | 1.2% | 3.8% | 1.0% |
>>>
>>> NOTE: The series applies on top of v6.11.
>>>
>>> Thanks,
>>> Ryan
>>>
>>>
>>> Ryan Roberts (57):
>>> mm: Add macros ahead of supporting boot-time page size selection
>>> vmlinux: Align to PAGE_SIZE_MAX
>>> mm/memcontrol: Fix seq_buf size to save memory when PAGE_SIZE is
>>> large
>>> mm/page_alloc: Make page_frag_cache boot-time page size compatible
>>> mm: Avoid split pmd ptl if pmd level is run-time folded
>>> mm: Remove PAGE_SIZE compile-time constant assumption
>>> fs: Introduce MAX_BUF_PER_PAGE_SIZE_MAX for array sizing
>>> fs: Remove PAGE_SIZE compile-time constant assumption
>>> fs/nfs: Remove PAGE_SIZE compile-time constant assumption
>>> fs/ext4: Remove PAGE_SIZE compile-time constant assumption
>>> fork: Permit boot-time THREAD_SIZE determination
>>> cgroup: Remove PAGE_SIZE compile-time constant assumption
>>> bpf: Remove PAGE_SIZE compile-time constant assumption
>>> pm/hibernate: Remove PAGE_SIZE compile-time constant assumption
>>> stackdepot: Remove PAGE_SIZE compile-time constant assumption
>>> perf: Remove PAGE_SIZE compile-time constant assumption
>>> kvm: Remove PAGE_SIZE compile-time constant assumption
>>> trace: Remove PAGE_SIZE compile-time constant assumption
>>> crash: Remove PAGE_SIZE compile-time constant assumption
>>> crypto: Remove PAGE_SIZE compile-time constant assumption
>>> sunrpc: Remove PAGE_SIZE compile-time constant assumption
>>> sound: Remove PAGE_SIZE compile-time constant assumption
>>> net: Remove PAGE_SIZE compile-time constant assumption
>>> net: fec: Remove PAGE_SIZE compile-time constant assumption
>>> net: marvell: Remove PAGE_SIZE compile-time constant assumption
>>> net: hns3: Remove PAGE_SIZE compile-time constant assumption
>>> net: e1000: Remove PAGE_SIZE compile-time constant assumption
>>> net: igbvf: Remove PAGE_SIZE compile-time constant assumption
>>> net: igb: Remove PAGE_SIZE compile-time constant assumption
>>> drivers/base: Remove PAGE_SIZE compile-time constant assumption
>>> edac: Remove PAGE_SIZE compile-time constant assumption
>>> optee: Remove PAGE_SIZE compile-time constant assumption
>>> random: Remove PAGE_SIZE compile-time constant assumption
>>> sata_sil24: Remove PAGE_SIZE compile-time constant assumption
>>> virtio: Remove PAGE_SIZE compile-time constant assumption
>>> xen: Remove PAGE_SIZE compile-time constant assumption
>>> arm64: Fix macros to work in C code in addition to the linker
>>> script
>>> arm64: Track early pgtable allocation limit
>>> arm64: Introduce macros required for boot-time page selection
>>> arm64: Refactor early pgtable size calculation macros
>>> arm64: Pass desired page size on command line
>>> arm64: Divorce early init from PAGE_SIZE
>>> arm64: Clean up simple cases of CONFIG_ARM64_*K_PAGES
>>> arm64: Align sections to PAGE_SIZE_MAX
>>> arm64: Rework trampoline rodata mapping
>>> arm64: Generalize fixmap for boot-time page size
>>> arm64: Statically allocate and align for worst-case page size
>>> arm64: Convert switch to if for non-const comparison values
>>> arm64: Convert BUILD_BUG_ON to VM_BUG_ON
>>> arm64: Remove PAGE_SZ asm-offset
>>> arm64: Introduce cpu features for page sizes
>>> arm64: Remove PAGE_SIZE from assembly code
>>> arm64: Runtime-fold pmd level
>>> arm64: Support runtime folding in idmap_kpti_install_ng_mappings
>>> arm64: TRAMP_VALIAS is no longer compile-time constant
>>> arm64: Determine THREAD_SIZE at boot-time
>>> arm64: Enable boot-time page size selection
>>>
>>> arch/alpha/include/asm/page.h | 1 +
>>> arch/arc/include/asm/page.h | 1 +
>>> arch/arm/include/asm/page.h | 1 +
>>> arch/arm64/Kconfig | 26 ++-
>>> arch/arm64/include/asm/assembler.h | 78 ++++++-
>>> arch/arm64/include/asm/cpufeature.h | 44 +++-
>>> arch/arm64/include/asm/efi.h | 2 +-
>>> arch/arm64/include/asm/fixmap.h | 28 ++-
>>> arch/arm64/include/asm/kernel-pgtable.h | 150 +++++++++----
>>> arch/arm64/include/asm/kvm_arm.h | 21 +-
>>> arch/arm64/include/asm/kvm_hyp.h | 11 +
>>> arch/arm64/include/asm/kvm_pgtable.h | 6 +-
>>> arch/arm64/include/asm/memory.h | 62 ++++--
>>> arch/arm64/include/asm/page-def.h | 3 +-
>>> arch/arm64/include/asm/pgalloc.h | 16 +-
>>> arch/arm64/include/asm/pgtable-geometry.h | 46 ++++
>>> arch/arm64/include/asm/pgtable-hwdef.h | 28 ++-
>>> arch/arm64/include/asm/pgtable-prot.h | 2 +-
>>> arch/arm64/include/asm/pgtable.h | 133 +++++++++---
>>> arch/arm64/include/asm/processor.h | 10 +-
>>> arch/arm64/include/asm/sections.h | 1 +
>>> arch/arm64/include/asm/smp.h | 1 +
>>> arch/arm64/include/asm/sparsemem.h | 15 +-
>>> arch/arm64/include/asm/sysreg.h | 54 +++--
>>> arch/arm64/include/asm/tlb.h | 3 +
>>> arch/arm64/kernel/asm-offsets.c | 4 +-
>>> arch/arm64/kernel/cpufeature.c | 93 ++++++--
>>> arch/arm64/kernel/efi.c | 2 +-
>>> arch/arm64/kernel/entry.S | 60 +++++-
>>> arch/arm64/kernel/head.S | 46 +++-
>>> arch/arm64/kernel/hibernate-asm.S | 6 +-
>>> arch/arm64/kernel/image-vars.h | 14 ++
>>> arch/arm64/kernel/image.h | 4 +
>>> arch/arm64/kernel/pi/idreg-override.c | 68 +++++-
>>> arch/arm64/kernel/pi/map_kernel.c | 165 ++++++++++----
>>> arch/arm64/kernel/pi/map_range.c | 201
>>> ++++++++++++++++--
>>> arch/arm64/kernel/pi/pi.h | 63 +++++-
>>> arch/arm64/kernel/relocate_kernel.S | 10 +-
>>> arch/arm64/kernel/vdso-wrap.S | 4 +-
>>> arch/arm64/kernel/vdso.c | 7 +-
>>> arch/arm64/kernel/vdso/vdso.lds.S | 4 +-
>>> arch/arm64/kernel/vdso32-wrap.S | 4 +-
>>> arch/arm64/kernel/vdso32/vdso.lds.S | 4 +-
>>> arch/arm64/kernel/vmlinux.lds.S | 48 +++--
>>> arch/arm64/kvm/arm.c | 10 +
>>> arch/arm64/kvm/hyp/nvhe/Makefile | 1 +
>>> arch/arm64/kvm/hyp/nvhe/host.S | 10 +-
>>> arch/arm64/kvm/hyp/nvhe/hyp.lds.S | 4 +-
>>> arch/arm64/kvm/hyp/nvhe/pgtable-geometry.c | 16 ++
>>> arch/arm64/kvm/mmu.c | 39 ++--
>>> arch/arm64/lib/clear_page.S | 7 +-
>>> arch/arm64/lib/copy_page.S | 33 ++-
>>> arch/arm64/lib/mte.S | 27 ++-
>>> arch/arm64/mm/Makefile | 1 +
>>> arch/arm64/mm/fixmap.c | 38 ++--
>>> arch/arm64/mm/hugetlbpage.c | 40 +---
>>> arch/arm64/mm/init.c | 26 +--
>>> arch/arm64/mm/kasan_init.c | 8 +-
>>> arch/arm64/mm/mmu.c | 53 +++--
>>> arch/arm64/mm/pgd.c | 12 +-
>>> arch/arm64/mm/pgtable-geometry.c | 24 +++
>>> arch/arm64/mm/proc.S | 128 ++++++++---
>>> arch/arm64/mm/ptdump.c | 3 +-
>>> arch/arm64/tools/cpucaps | 3 +
>>> arch/csky/include/asm/page.h | 3 +
>>> arch/hexagon/include/asm/page.h | 2 +
>>> arch/loongarch/include/asm/page.h | 2 +
>>> arch/m68k/include/asm/page.h | 1 +
>>> arch/microblaze/include/asm/page.h | 1 +
>>> arch/mips/include/asm/page.h | 1 +
>>> arch/nios2/include/asm/page.h | 2 +
>>> arch/openrisc/include/asm/page.h | 1 +
>>> arch/parisc/include/asm/page.h | 1 +
>>> arch/powerpc/include/asm/page.h | 2 +
>>> arch/riscv/include/asm/page.h | 1 +
>>> arch/s390/include/asm/page.h | 1 +
>>> arch/sh/include/asm/page.h | 1 +
>>> arch/sparc/include/asm/page.h | 3 +
>>> arch/um/include/asm/page.h | 2 +
>>> arch/x86/include/asm/page_types.h | 2 +
>>> arch/xtensa/include/asm/page.h | 1 +
>>> crypto/lskcipher.c | 4 +-
>>> drivers/ata/sata_sil24.c | 46 ++--
>>> drivers/base/node.c | 6 +-
>>> drivers/base/topology.c | 32 +--
>>> drivers/block/virtio_blk.c | 2 +-
>>> drivers/char/random.c | 4 +-
>>> drivers/edac/edac_mc.h | 13 +-
>>> drivers/firmware/efi/libstub/arm64.c | 3 +-
>>> drivers/irqchip/irq-gic-v3-its.c | 2 +-
>>> drivers/mtd/mtdswap.c | 4 +-
>>> drivers/net/ethernet/freescale/fec.h | 3 +-
>>> drivers/net/ethernet/freescale/fec_main.c | 5 +-
>>> .../net/ethernet/hisilicon/hns3/hns3_enet.h | 4 +-
>>> drivers/net/ethernet/intel/e1000/e1000_main.c | 6 +-
>>> drivers/net/ethernet/intel/igb/igb.h | 25 +--
>>> drivers/net/ethernet/intel/igb/igb_main.c | 149 +++++++------
>>> drivers/net/ethernet/intel/igbvf/netdev.c | 6 +-
>>> drivers/net/ethernet/marvell/mvneta.c | 9 +-
>>> drivers/net/ethernet/marvell/sky2.h | 2 +-
>>> drivers/tee/optee/call.c | 7 +-
>>> drivers/tee/optee/smc_abi.c | 2 +-
>>> drivers/virtio/virtio_balloon.c | 10 +-
>>> drivers/xen/balloon.c | 11 +-
>>> drivers/xen/biomerge.c | 12 +-
>>> drivers/xen/privcmd.c | 2 +-
>>> drivers/xen/xenbus/xenbus_client.c | 5 +-
>>> drivers/xen/xlate_mmu.c | 6 +-
>>> fs/binfmt_elf.c | 11 +-
>>> fs/buffer.c | 2 +-
>>> fs/coredump.c | 8 +-
>>> fs/ext4/ext4.h | 36 ++--
>>> fs/ext4/move_extent.c | 2 +-
>>> fs/ext4/readpage.c | 2 +-
>>> fs/fat/dir.c | 4 +-
>>> fs/fat/fatent.c | 4 +-
>>> fs/nfs/nfs42proc.c | 2 +-
>>> fs/nfs/nfs42xattr.c | 2 +-
>>> fs/nfs/nfs4proc.c | 2 +-
>>> include/asm-generic/pgtable-geometry.h | 71 +++++++
>>> include/asm-generic/vmlinux.lds.h | 38 ++--
>>> include/linux/buffer_head.h | 1 +
>>> include/linux/cpumask.h | 5 +
>>> include/linux/linkage.h | 4 +-
>>> include/linux/mm.h | 17 +-
>>> include/linux/mm_types.h | 15 +-
>>> include/linux/mm_types_task.h | 2 +-
>>> include/linux/mmzone.h | 3 +-
>>> include/linux/netlink.h | 6 +-
>>> include/linux/percpu-defs.h | 4 +-
>>> include/linux/perf_event.h | 2 +-
>>> include/linux/sched.h | 4 +-
>>> include/linux/slab.h | 7 +-
>>> include/linux/stackdepot.h | 6 +-
>>> include/linux/sunrpc/svc.h | 8 +-
>>> include/linux/sunrpc/svc_rdma.h | 4 +-
>>> include/linux/sunrpc/svcsock.h | 2 +-
>>> include/linux/swap.h | 17 +-
>>> include/linux/swapops.h | 6 +-
>>> include/linux/thread_info.h | 10 +-
>>> include/xen/page.h | 2 +
>>> init/main.c | 7 +-
>>> kernel/bpf/core.c | 9 +-
>>> kernel/bpf/ringbuf.c | 54 ++---
>>> kernel/cgroup/cgroup.c | 8 +-
>>> kernel/crash_core.c | 2 +-
>>> kernel/events/core.c | 2 +-
>>> kernel/fork.c | 71 +++----
>>> kernel/power/power.h | 2 +-
>>> kernel/power/snapshot.c | 2 +-
>>> kernel/power/swap.c | 129 +++++++++--
>>> kernel/trace/fgraph.c | 2 +-
>>> kernel/trace/trace.c | 2 +-
>>> lib/stackdepot.c | 6 +-
>>> mm/kasan/report.c | 3 +-
>>> mm/memcontrol.c | 11 +-
>>> mm/memory.c | 4 +-
>>> mm/mmap.c | 2 +-
>>> mm/page-writeback.c | 2 +-
>>> mm/page_alloc.c | 31 +--
>>> mm/slub.c | 2 +-
>>> mm/sparse.c | 2 +-
>>> mm/swapfile.c | 2 +-
>>> mm/vmalloc.c | 7 +-
>>> net/9p/trans_virtio.c | 4 +-
>>> net/core/hotdata.c | 4 +-
>>> net/core/skbuff.c | 4 +-
>>> net/core/sysctl_net_core.c | 2 +-
>>> net/sunrpc/cache.c | 3 +-
>>> net/unix/af_unix.c | 2 +-
>>> sound/soc/soc-utils.c | 4 +-
>>> virt/kvm/kvm_main.c | 2 +-
>>> 172 files changed, 2185 insertions(+), 951 deletions(-)
>>> create mode 100644 arch/arm64/include/asm/pgtable-geometry.h
>>> create mode 100644 arch/arm64/kvm/hyp/nvhe/pgtable-geometry.c
>>> create mode 100644 arch/arm64/mm/pgtable-geometry.c
>>> create mode 100644 include/asm-generic/pgtable-geometry.h
>>>
>>> --
>>> 2.43.0
>>>
>>>
>>
>> Hi Ryan,
>>
>> First off, this is excellent work! Your cover page was very detailed
>> and made the patch set easier to understand.
>>
>> Some questions/comments:
>>
>> Once a kernel is booted with a certain page size, could there be issues
>> if it is booted later with a different page size? How about if this is
>> done frequently?
>
> I think that is the reason why you are only given the option in RHEL
> to select the kernel (4K vs. 64K) to use at install time.
>
> Software can easily use a different data format for persistance based
> on the base page size. I would suspect DBs might be the usual suspects.
>
> One example is swap space I think, where the base page size used when
> formatting the device is used, and it cannot be used with a different
> page size unless reformatting it.
>
> So ... one has to be a bit careful ...
>
Yes, that is what I was thinking. Once a userspace process does an I/O
and if it is based on PAGE_SIZE things can go south. I think this is
not an issue with THP, so maybe it's possible with boot-time page selection?
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