Re: [PATCH v2 0/4] Speed up boot with faster linear map creation

[Itaru Kitayama <itaru.kitayama@linux.dev>]

Hi Ryan,

On Sat, Apr 06, 2024 at 09:32:34AM +0100, Ryan Roberts wrote:
> Hi Itaru,
> 
> On 05/04/2024 08:39, Itaru Kitayama wrote:
> > On Thu, Apr 04, 2024 at 03:33:04PM +0100, Ryan Roberts wrote:
> >> Hi All,
> >>
> >> It turns out that creating the linear map can take a significant proportion of
> >> the total boot time, especially when rodata=full. And most of the time is spent
> >> waiting on superfluous tlb invalidation and memory barriers. This series reworks
> >> the kernel pgtable generation code to significantly reduce the number of those
> >> TLBIs, ISBs and DSBs. See each patch for details.
> >>
> >> The below shows the execution time of map_mem() across a couple of different
> >> systems with different RAM configurations. We measure after applying each patch
> >> and show the improvement relative to base (v6.9-rc2):
> >>
> >>                | Apple M2 VM | Ampere Altra| Ampere Altra| Ampere Altra
> >>                | VM, 16G     | VM, 64G     | VM, 256G    | Metal, 512G
> >> ---------------|-------------|-------------|-------------|-------------
> >>                |   ms    (%) |   ms    (%) |   ms    (%) |    ms    (%)
> >> ---------------|-------------|-------------|-------------|-------------
> >> base           |  153   (0%) | 2227   (0%) | 8798   (0%) | 17442   (0%)
> >> no-cont-remap  |   77 (-49%) |  431 (-81%) | 1727 (-80%) |  3796 (-78%)
> >> batch-barriers |   13 (-92%) |  162 (-93%) |  655 (-93%) |  1656 (-91%)
> >> no-alloc-remap |   11 (-93%) |  109 (-95%) |  449 (-95%) |  1257 (-93%)
> >> lazy-unmap     |    6 (-96%) |   61 (-97%) |  257 (-97%) |   838 (-95%)
> >>
> >> This series applies on top of v6.9-rc2. All mm selftests pass. I've compile and
> >> boot tested various PAGE_SIZE and VA size configs.
> >>
> >> ---
> >>
> >> Changes since v1 [1]
> >> ====================
> >>
> >>   - Added Tested-by tags (thanks to Eric and Itaru)
> >>   - Renamed ___set_pte() -> __set_pte_nosync() (per Ard)
> >>   - Reordered patches (biggest impact & least controversial first)
> >>   - Reordered alloc/map/unmap functions in mmu.c to aid reader
> >>   - pte_clear() -> __pte_clear() in clear_fixmap_nosync()
> >>   - Reverted generic p4d_index() which caused x86 build error. Replaced with
> >>     unconditional p4d_index() define under arm64.
> >>
> >>
> >> [1] https://lore.kernel.org/linux-arm-kernel/20240326101448.3453626-1-ryan.roberts@arm.com/
> >>
> >> Thanks,
> >> Ryan
> >>
> >>
> >> Ryan Roberts (4):
> >>   arm64: mm: Don't remap pgtables per-cont(pte|pmd) block
> >>   arm64: mm: Batch dsb and isb when populating pgtables
> >>   arm64: mm: Don't remap pgtables for allocate vs populate
> >>   arm64: mm: Lazily clear pte table mappings from fixmap
> >>
> >>  arch/arm64/include/asm/fixmap.h  |   5 +-
> >>  arch/arm64/include/asm/mmu.h     |   8 +
> >>  arch/arm64/include/asm/pgtable.h |  13 +-
> >>  arch/arm64/kernel/cpufeature.c   |  10 +-
> >>  arch/arm64/mm/fixmap.c           |  11 +
> >>  arch/arm64/mm/mmu.c              | 377 +++++++++++++++++++++++--------
> >>  6 files changed, 319 insertions(+), 105 deletions(-)
> >>
> >> --
> >> 2.25.1
> >>
> > 
> > I've build and boot tested the v2 on FVP, base is taken from your
> > linux-rr repo. Running run_vmtests.sh on v2 left some gup longterm not oks, would you take a look at it? The mm ksefltests used is from your linux-rr repo too.
> 
> Thanks for taking a look at this.
> 
> I can't reproduce your issue unfortunately; steps as follows on Apple M2 VM:
> 
> Config: arm64 defconfig + the following:
> 
> # Squashfs for snaps, xfs for large file folios.
> ./scripts/config --enable CONFIG_SQUASHFS_LZ4
> ./scripts/config --enable CONFIG_SQUASHFS_LZO
> ./scripts/config --enable CONFIG_SQUASHFS_XZ
> ./scripts/config --enable CONFIG_SQUASHFS_ZSTD
> ./scripts/config --enable CONFIG_XFS_FS
> 
> # For general mm debug.
> ./scripts/config --enable CONFIG_DEBUG_VM
> ./scripts/config --enable CONFIG_DEBUG_VM_MAPLE_TREE
> ./scripts/config --enable CONFIG_DEBUG_VM_RB
> ./scripts/config --enable CONFIG_DEBUG_VM_PGFLAGS
> ./scripts/config --enable CONFIG_DEBUG_VM_PGTABLE
> ./scripts/config --enable CONFIG_PAGE_TABLE_CHECK
> 
> # For mm selftests.
> ./scripts/config --enable CONFIG_USERFAULTFD
> ./scripts/config --enable CONFIG_TEST_VMALLOC
> ./scripts/config --enable CONFIG_GUP_TEST
> 
> Running on VM with 12G memory, split across 2 (emulated) NUMA nodes (needed by
> some mm selftests), with kernel command line to reserve hugetlbs and other
> features required by some mm selftests:
> 
> "
> transparent_hugepage=madvise earlycon root=/dev/vda2 secretmem.enable
> hugepagesz=1G hugepages=0:2,1:2 hugepagesz=32M hugepages=0:2,1:2
> default_hugepagesz=2M hugepages=0:64,1:64 hugepagesz=64K hugepages=0:2,1:2
> "
> 
> Ubuntu userspace running off XFS rootfs. Build and run mm selftests from same
> git tree.
> 
> 
> Although I don't think any of this config should make a difference to gup_longterm.
> 
> Looks like your errors are all "ftruncate() failed". I've seen this problem on
> our CI system. There it is due to running the tests from NFS file system. What
> filesystem are you using? Perhaps you are sharing into the FVP using 9p? That
> might also be problematic.

That was it. This time I booted up the kernel including your series on
QEMU on my M1 and executed the gup_longterm program without the ftruncate
failures. When testing your kernel on FVP, I was executing the script from the FVP's host filesystem using 9p.

Thanks,
Itaru.

> 
> Does this problem reproduce with v6.9-rc2, without my patches? I except it
> probably does?
> 
> Thanks,
> Ryan
> 
> > 
> > Thanks,
> > Itaru.
> 

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