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

[Itaru Kitayama]

Hi Ryan,

> On Apr 8, 2024, at 16:30, Ryan Roberts <ryan.roberts@xxxxxxx> wrote:
> 
> On 06/04/2024 11:31, Itaru Kitayama wrote:
>> 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@xxxxxxx/
>>>>> 
>>>>> 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.
> 
> I'm not sure exactly what the root cause is. Perhaps there isn't enough space on
> the disk? It might be worth enhancing the error log to provide the errno in
> tools/testing/selftests/mm/gup_longterm.c.
> 

Attached is the strace’d gup_longterm executiong log on your pgtable-boot-speedup-v2 kernel.

Thanks,
Itaru.

Attachment: straced-gup_longterm.log
Description: Binary data

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