Message-ID: <c2ab8854-66f9-4b26-bcbc-c138918f0e91@redhat.com>
Date: Wed, 10 Apr 2024 09:10:51 +0200
From: David Hildenbrand <david@...hat.com>
To: Itaru Kitayama <itaru.kitayama@...ux.dev>
Cc: Ryan Roberts <ryan.roberts@....com>,
 Catalin Marinas <Catalin.Marinas@....com>, Will Deacon <will@...nel.org>,
 Mark Rutland <Mark.Rutland@....com>, Ard Biesheuvel <ardb@...nel.org>,
 Donald Dutile <ddutile@...hat.com>, Eric Chanudet <echanude@...hat.com>,
 Linux ARM <linux-arm-kernel@...ts.infradead.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 0/4] Speed up boot with faster linear map creation

On 10.04.24 08:47, Itaru Kitayama wrote:
> 
> 
>> On Apr 10, 2024, at 8:30, Itaru Kitayama <itaru.kitayama@...ux.dev> wrote:
>>
>> Hi David,
>>
>>> On Apr 9, 2024, at 23:45, David Hildenbrand <david@...hat.com> wrote:
>>>
>>> On 09.04.24 16:39, Ryan Roberts wrote:
>>>> On 09/04/2024 15:29, David Hildenbrand wrote:
>>>>> On 09.04.24 16:13, Ryan Roberts wrote:
>>>>>> On 09/04/2024 12:51, David Hildenbrand wrote:
>>>>>>> On 09.04.24 13:29, David Hildenbrand wrote:
>>>>>>>> On 09.04.24 13:22, David Hildenbrand wrote:
>>>>>>>>> On 09.04.24 12:13, Itaru Kitayama wrote:
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>> On Apr 9, 2024, at 19:04, Ryan Roberts <ryan.roberts@....com> wrote:
>>>>>>>>>>>
>>>>>>>>>>> On 09/04/2024 01:10, Itaru Kitayama wrote:
>>>>>>>>>>>> Hi Ryan,
>>>>>>>>>>>>
>>>>>>>>>>>>> On Apr 8, 2024, at 16:30, Ryan Roberts <ryan.roberts@....com> 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@arm.com/<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.
>>>>>>>>>>>>>
>>>>>>>>>>>>> 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.
>>>>>>>>>>>
>>>>>>>>>>> Sorry are you saying that it only fails with the pgtable-boot-speedup-v2
>>>>>>>>>>> patch
>>>>>>>>>>> set applied? I thought we previously concluded that it was independent of
>>>>>>>>>>> that?
>>>>>>>>>>> I was under the impression that it was filesystem related and not something
>>>>>>>>>>> that
>>>>>>>>>>> I was planning to investigate.
>>>>>>>>>>
>>>>>>>>>> No, irrespective of the kernel, if using 9p on FVP the test program fails.
>>>>>>>>>> It is indeed 9p filesystem related, as I switched to using NFS all the
>>>>>>>>>> issues are gone.
>>>>>>>>>
>>>>>>>>> Did it never work on 9p? If so, we might have to SKIP that test.
>>>>>>>>>
>>>>>>>>> openat(AT_FDCWD, "gup_longterm.c_tmpfile_BLboOt", O_RDWR|O_CREAT|O_EXCL,
>>>>>>>>> 0600) = 3
>>>>>>>>> unlinkat(AT_FDCWD, "gup_longterm.c_tmpfile_BLboOt", 0) = 0
>>>>>>>>> fstatfs(3, 0xffffe505a840)              = -1 EOPNOTSUPP (Operation not
>>>>>>>>> supported)
>>>>>>>>> ftruncate(3, 4096)                      = -1 ENOENT (No such file or
>>>>>>>>> directory)
>>>>>>>>
>>>>>>>> Note: I'm wondering if the unlinkat here is the problem that makes
>>>>>>>> ftruncate() with 9p result in weird errors (e.g., the hypervisor
>>>>>>>> unlinked the file and cannot reopen it for the fstatfs/ftruncate. ...
>>>>>>>> which gives us weird errors here).
>>>>>>>>
>>>>>>>> Then, we should lookup the fs type in run_with_local_tmpfile() before
>>>>>>>> the unlink() and simply skip the test if it is 9p.
>>>>>>>
>>>>>>> The unlink with 9p most certainly was a known issue in the past:
>>>>>>>
>>>>>>> https://gitlab.com/qemu-project/qemu/-/issues/103
>>>>>>>
>>>>>>> Maybe it's still an issue with older hypervisors (QEMU?)? Or it was never
>>>>>>> completely resolved?
>>>>>>
>>>>>> I believe Itaru is running on FVP (Fixed Virtual Platform - "fast model" -
>>>>>> Arm's architecture emulator). So QEMU won't be involved here. The FVP emulates
>>>>>> a 9p device, so perhaps the bug is in there.
>>>>>
>>>>> Very likely.
>>>>>
>>>>>>
>>>>>> Note that I see lots of "fallocate() failed" failures in gup_longterm when
>>>>>> running on our CI system. This is a completely different setup; Real HW with
>>>>>> Linux running bare metal using an NFS rootfs. I'm not sure if this is related.
>>>>>> Logs show it failing consistently for the "tmpfile" and "local tmpfile" test
>>>>>> configs. I also see a couple of these fails in the cow tests.
>>>>>
>>>>> What is the fallocate() errno you are getting? strace log would help (to see if
>>>>> statfs also fails already)! Likely a similar NFS issue.
>>>> Unfortunately this is a system I don't have access to. I've requested some of
>>>> this triage to be done, but its fairly low priority unfortunately.
>>>
>>> To work around these BUGs (?) elsewhere, we could simply skip the test if get_fs_type() is not able to detect the FS type. Likely that's an early indicator that the unlink() messed something up.
>>>
>>> ... doesn't feel right, though.
>>
>> I think it’s a good idea so that the mm kselftests results look reasonable.

Yeah, but this will hide BUGs elsewhere. I suspect that in Ryan's NFS setup is
also a BUG lurking somewhere in the NFS implementation. But that's just a guess
until we have more details.

>> Since you’re an expert on GUP-fast (or fast-GUP?), when you update the code, could you print out errno as well like the split_huge_page_test.c does

While we could, I don't see much value in that for selftests. strace log is of much
more valuable to understand what is actually happening (e.g., fstatfs failing), and
quite easy to obtain.

>> Thanks,
>> Itaru.
> 
> David, attached is the straced execution log of the gup_longterm kselftest over the NFS case.
> I’m running the program on FVP, let me know if you need other logs or test results.

For your run, it all looks good:

openat(AT_FDCWD, "/tmp", O_RDWR|O_EXCL|O_TMPFILE, 0600) = 3
fcntl(3, F_GETFL)                       = 0x424002 (flags O_RDWR|O_LARGEFILE|O_TMPFILE)
fstatfs(3, {f_type=TMPFS_MAGIC, f_bsize=4096, f_blocks=416015, f_bfree=415997, f_bavail=415997, f_files=416015, f_ffree=416009, f_fsid={val=[0x8e6b7ce6, 0xe1737440]}, f_namelen=255, f_frsize=4096, f_flags=ST_VALID|ST_RELATIME}) = 0
ftruncate(3, 4096)                      = 0
fallocate(3, 0, 0, 4096)                = 0

-> TMPFS/SHMEM, works as expected

openat(AT_FDCWD, "gup_longterm.c_tmpfile_WMLTNf", O_RDWR|O_CREAT|O_EXCL, 0600) = 3
unlinkat(AT_FDCWD, "gup_longterm.c_tmpfile_WMLTNf", 0) = 0
fstatfs(3, {f_type=NFS_SUPER_MAGIC, f_bsize=1048576, f_blocks=112200, f_bfree=27954, f_bavail=23296, f_files=7307264, f_ffree=4724815, f_fsid={val=[0, 0]}, f_namelen=255, f_frsize=1048576, f_flags=ST_VALID|ST_RELATIME}) = 0
ftruncate(3, 4096)                      = 0
fallocate(3, 0, 0, 4096)                = 0

-> NFS, works as expected

Note that you get all skips (not fails), because your kernel is not compiled with CONFIG_GUP_TEST.

ok 1 # SKIP gup_test not available

-- 
Cheers,

David / dhildenb

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