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Message-ID: <fcc5b090-2f9a-4c7c-870a-6ef810111bee@arm.com>
Date: Wed, 30 Apr 2025 12:37:39 +0530
From: Dev Jain <dev.jain@....com>
To: Lance Yang <lance.yang@...ux.dev>,
Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: akpm@...ux-foundation.org, ryan.roberts@....com, david@...hat.com,
willy@...radead.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
catalin.marinas@....com, will@...nel.org, Liam.Howlett@...cle.com,
vbabka@...e.cz, jannh@...gle.com, anshuman.khandual@....com,
peterx@...hat.com, joey.gouly@....com, ioworker0@...il.com,
baohua@...nel.org, kevin.brodsky@....com, quic_zhenhuah@...cinc.com,
christophe.leroy@...roup.eu, yangyicong@...ilicon.com,
linux-arm-kernel@...ts.infradead.org, namit@...are.com, hughd@...gle.com,
yang@...amperecomputing.com, ziy@...dia.com
Subject: Re: [PATCH v2 0/7] Optimize mprotect for large folios
On 30/04/25 11:52 am, Lance Yang wrote:
>
>
> On 2025/4/30 13:42, Dev Jain wrote:
>>
>>
>> On 29/04/25 4:11 pm, Lorenzo Stoakes wrote:
>>> FWIW can confirm the same thing. Lance's fixes sort most of it out,
>>> but I also
>>> get this error:
>
> Good catch!
>
>>>
>>> mm/mprotect.c: In function ‘can_change_ptes_writable’:
>>> mm/mprotect.c:46:22: error: unused variable ‘page’ [-Werror=unused-
>>> variable]
>>> 46 | struct page *page;
>>> | ^~~~
>>>
>>> So you also need to remove this unused variable at the stop of
>>> can_change_ptes_writable().
>>
>> Strange that my build didn't catch this.
>
> Well, to catch unused variable warnings with GCC, enable stricter
> checks by passing -Wunused-variable via KCFLAGS, and use -Werror=unused-
> variable
> to force the build to fail if any variable is declared but unused:
>
> make -j$(nproc) KCFLAGS="-Wunused-variable -Werror=unused-variable"
I thought this was the default, but thanks Lance!
>
> Thanks,
> Lance
>
>
>>
>>>
>>> Cheers, Lorenzo
>>>
>>> On Tue, Apr 29, 2025 at 02:32:59PM +0530, Dev Jain wrote:
>>>>
>>>>
>>>> On 29/04/25 12:36 pm, Lance Yang wrote:
>>>>> Hey Dev,
>>>>>
>>>>> Hmm... I also hit the same compilation errors:
>>>>>
>>>>> In file included from ./include/linux/kasan.h:37,
>>>>> from ./include/linux/slab.h:260,
>>>>> from ./include/linux/crypto.h:19,
>>>>> from arch/x86/kernel/asm-offsets.c:9:
>>>>> ./include/linux/pgtable.h: In function ‘modify_prot_start_ptes’:
>>>>> ./include/linux/pgtable.h:905:15: error: implicit declaration of
>>>>> function ‘ptep_modify_prot_start’
>>>>> [-Werror=implicit-function-declaration]
>>>>> 905 | pte = ptep_modify_prot_start(vma, addr, ptep);
>>>>> | ^~~~~~~~~~~~~~~~~~~~~~
>>>>> ./include/linux/pgtable.h:905:15: error: incompatible types when
>>>>> assigning to type ‘pte_t’ from type ‘int’
>>>>> ./include/linux/pgtable.h:909:27: error: incompatible types when
>>>>> assigning to type ‘pte_t’ from type ‘int’
>>>>> 909 | tmp_pte = ptep_modify_prot_start(vma,
>>>>> addr, ptep);
>>>>> | ^~~~~~~~~~~~~~~~~~~~~~
>>>>> ./include/linux/pgtable.h: In function ‘modify_prot_commit_ptes’:
>>>>> ./include/linux/pgtable.h:925:17: error: implicit declaration of
>>>>> function ‘ptep_modify_prot_commit’
>>>>> [-Werror=implicit-function-declaration]
>>>>> 925 | ptep_modify_prot_commit(vma, addr, ptep,
>>>>> old_pte, pte);
>>>>> | ^~~~~~~~~~~~~~~~~~~~~~~
>>>>> ./include/linux/pgtable.h: At top level:
>>>>> ./include/linux/pgtable.h:1360:21: error: conflicting types for
>>>>> ‘ptep_modify_prot_start’; have ‘pte_t(struct vm_area_struct *, long
>>>>> unsigned int, pte_t *)’
>>>>> 1360 | static inline pte_t ptep_modify_prot_start(struct
>>>>> vm_area_struct *vma,
>>>>> | ^~~~~~~~~~~~~~~~~~~~~~
>>>>> ./include/linux/pgtable.h:905:15: note: previous implicit
>>>>> declaration of
>>>>> ‘ptep_modify_prot_start’ with type ‘int()’
>>>>> 905 | pte = ptep_modify_prot_start(vma, addr, ptep);
>>>>> | ^~~~~~~~~~~~~~~~~~~~~~
>>>>> ./include/linux/pgtable.h:1371:20: warning: conflicting types for
>>>>> ‘ptep_modify_prot_commit’; have ‘void(struct vm_area_struct *, long
>>>>> unsigned int, pte_t *, pte_t, pte_t)’
>>>>> 1371 | static inline void ptep_modify_prot_commit(struct
>>>>> vm_area_struct *vma,
>>>>> | ^~~~~~~~~~~~~~~~~~~~~~~
>>>>> ./include/linux/pgtable.h:1371:20: error: static declaration of
>>>>> ‘ptep_modify_prot_commit’ follows non-static declaration
>>>>> ./include/linux/pgtable.h:925:17: note: previous implicit
>>>>> declaration of
>>>>> ‘ptep_modify_prot_commit’ with type ‘void(struct vm_area_struct *,
>>>>> long
>>>>> unsigned int, pte_t *, pte_t, pte_t)’
>>>>> 925 | ptep_modify_prot_commit(vma, addr, ptep,
>>>>> old_pte, pte);
>>>>> | ^~~~~~~~~~~~~~~~~~~~~~~
>>>>> CC /home/runner/work/mm-test-robot/mm-test-robot/linux/tools/
>>>>> objtool/
>>>>> libstring.o
>>>>> CC /home/runner/work/mm-test-robot/mm-test-robot/linux/tools/
>>>>> objtool/
>>>>> libctype.o
>>>>> CC /home/runner/work/mm-test-robot/mm-test-robot/linux/tools/
>>>>> objtool/
>>>>> str_error_r.o
>>>>> CC /home/runner/work/mm-test-robot/mm-test-robot/linux/tools/
>>>>> objtool/
>>>>> librbtree.o
>>>>> cc1: some warnings being treated as errors
>>>>> make[2]: *** [scripts/Makefile.build:98: arch/x86/kernel/asm-
>>>>> offsets.s]
>>>>> Error 1
>>>>> make[1]: *** [/home/runner/work/mm-test-robot/mm-test-robot/linux/
>>>>> Makefile:1280: prepare0] Error 2
>>>>> make[1]: *** Waiting for unfinished jobs....
>>>>> LD /home/runner/work/mm-test-robot/mm-test-robot/linux/tools/
>>>>> objtool/
>>>>> objtool-in.o
>>>>> LINK /home/runner/work/mm-test-robot/mm-test-robot/linux/tools/
>>>>> objtool/objtool
>>>>> make: *** [Makefile:248: __sub-make] Error 2
>>>>>
>>>>> Well, modify_prot_start_ptes() calls ptep_modify_prot_start(), but x86
>>>>> does not define __HAVE_ARCH_PTEP_MODIFY_PROT_TRANSACTION. To avoid
>>>>> implicit declaration errors, the architecture-independent
>>>>> ptep_modify_prot_start() must be defined before
>>>>> modify_prot_start_ptes().
>>>>>
>>>>> With the changes below, things work correctly now ;)
>>>>
>>>> Ah thanks! My bad :(
>>>>
>>>>>
>>>>> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
>>>>> index 10cdb87ccecf..d9d6c49bb914 100644
>>>>> --- a/include/linux/pgtable.h
>>>>> +++ b/include/linux/pgtable.h
>>>>> @@ -895,44 +895,6 @@ static inline void wrprotect_ptes(struct
>>>>> mm_struct
>>>>> *mm, unsigned long addr,
>>>>> }
>>>>> #endif
>>>>>
>>>>> -/* See the comment for ptep_modify_prot_start */
>>>>> -#ifndef modify_prot_start_ptes
>>>>> -static inline pte_t modify_prot_start_ptes(struct vm_area_struct
>>>>> *vma,
>>>>> - unsigned long addr, pte_t *ptep, unsigned int nr)
>>>>> -{
>>>>> - pte_t pte, tmp_pte;
>>>>> -
>>>>> - pte = ptep_modify_prot_start(vma, addr, ptep);
>>>>> - while (--nr) {
>>>>> - ptep++;
>>>>> - addr += PAGE_SIZE;
>>>>> - tmp_pte = ptep_modify_prot_start(vma, addr, ptep);
>>>>> - if (pte_dirty(tmp_pte))
>>>>> - pte = pte_mkdirty(pte);
>>>>> - if (pte_young(tmp_pte))
>>>>> - pte = pte_mkyoung(pte);
>>>>> - }
>>>>> - return pte;
>>>>> -}
>>>>> -#endif
>>>>> -
>>>>> -/* See the comment for ptep_modify_prot_commit */
>>>>> -#ifndef modify_prot_commit_ptes
>>>>> -static inline void modify_prot_commit_ptes(struct vm_area_struct
>>>>> *vma,
>>>>> unsigned long addr,
>>>>> - pte_t *ptep, pte_t old_pte, pte_t pte, unsigned int nr)
>>>>> -{
>>>>> - for (;;) {
>>>>> - ptep_modify_prot_commit(vma, addr, ptep, old_pte, pte);
>>>>> - if (--nr == 0)
>>>>> - break;
>>>>> - ptep++;
>>>>> - addr += PAGE_SIZE;
>>>>> - old_pte = pte_next_pfn(old_pte);
>>>>> - pte = pte_next_pfn(pte);
>>>>> - }
>>>>> -}
>>>>> -#endif
>>>>> -
>>>>> /*
>>>>> * On some architectures hardware does not set page access bit when
>>>>> accessing
>>>>> * memory page, it is responsibility of software setting this
>>>>> bit. It
>>>>> brings
>>>>> @@ -1375,6 +1337,45 @@ static inline void
>>>>> ptep_modify_prot_commit(struct
>>>>> vm_area_struct *vma,
>>>>> __ptep_modify_prot_commit(vma, addr, ptep, pte);
>>>>> }
>>>>> #endif /* __HAVE_ARCH_PTEP_MODIFY_PROT_TRANSACTION */
>>>>> +
>>>>> +/* See the comment for ptep_modify_prot_start */
>>>>> +#ifndef modify_prot_start_ptes
>>>>> +static inline pte_t modify_prot_start_ptes(struct vm_area_struct
>>>>> *vma,
>>>>> + unsigned long addr, pte_t *ptep, unsigned int nr)
>>>>> +{
>>>>> + pte_t pte, tmp_pte;
>>>>> +
>>>>> + pte = ptep_modify_prot_start(vma, addr, ptep);
>>>>> + while (--nr) {
>>>>> + ptep++;
>>>>> + addr += PAGE_SIZE;
>>>>> + tmp_pte = ptep_modify_prot_start(vma, addr, ptep);
>>>>> + if (pte_dirty(tmp_pte))
>>>>> + pte = pte_mkdirty(pte);
>>>>> + if (pte_young(tmp_pte))
>>>>> + pte = pte_mkyoung(pte);
>>>>> + }
>>>>> + return pte;
>>>>> +}
>>>>> +#endif
>>>>> +
>>>>> +/* See the comment for ptep_modify_prot_commit */
>>>>> +#ifndef modify_prot_commit_ptes
>>>>> +static inline void modify_prot_commit_ptes(struct vm_area_struct
>>>>> *vma,
>>>>> unsigned long addr,
>>>>> + pte_t *ptep, pte_t old_pte, pte_t pte, unsigned int nr)
>>>>> +{
>>>>> + for (;;) {
>>>>> + ptep_modify_prot_commit(vma, addr, ptep, old_pte, pte);
>>>>> + if (--nr == 0)
>>>>> + break;
>>>>> + ptep++;
>>>>> + addr += PAGE_SIZE;
>>>>> + old_pte = pte_next_pfn(old_pte);
>>>>> + pte = pte_next_pfn(pte);
>>>>> + }
>>>>> +}
>>>>> +#endif
>>>>> +
>>>>> #endif /* CONFIG_MMU */
>>>>>
>>>>> /*
>>>>> --
>>>>>
>>>>> Thanks,
>>>>> Lance
>>>>>
>>>>> On 2025/4/29 13:23, Dev Jain wrote:
>>>>>> This patchset optimizes the mprotect() system call for large folios
>>>>>> by PTE-batching.
>>>>>>
>>>>>> We use the following test cases to measure performance,
>>>>>> mprotect()'ing
>>>>>> the mapped memory to read-only then read-write 40 times:
>>>>>>
>>>>>> Test case 1: Mapping 1G of memory, touching it to get PMD-THPs, then
>>>>>> pte-mapping those THPs
>>>>>> Test case 2: Mapping 1G of memory with 64K mTHPs
>>>>>> Test case 3: Mapping 1G of memory with 4K pages
>>>>>>
>>>>>> Average execution time on arm64, Apple M3:
>>>>>> Before the patchset:
>>>>>> T1: 7.9 seconds T2: 7.9 seconds T3: 4.2 seconds
>>>>>>
>>>>>> After the patchset:
>>>>>> T1: 2.1 seconds T2: 2.2 seconds T3: 4.2 seconds
>>>>>>
>>>>>> Observing T1/T2 and T3 before the patchset, we also remove the
>>>>>> regression
>>>>>> introduced by ptep_get() on a contpte block. And, for large folios
>>>>>> we get
>>>>>> an almost 74% performance improvement.
>>>>>>
>>>>>> v1->v2:
>>>>>> - Rebase onto mm-unstable (6ebffe676fcf: util_macros.h: make the
>>>>>> header more resilient)
>>>>>> - Abridge the anon-exclusive condition (Lance Yang)
>>>>>>
>>>>>> Dev Jain (7):
>>>>>> mm: Refactor code in mprotect
>>>>>> mm: Optimize mprotect() by batch-skipping PTEs
>>>>>> mm: Add batched versions of ptep_modify_prot_start/commit
>>>>>> arm64: Add batched version of ptep_modify_prot_start
>>>>>> arm64: Add batched version of ptep_modify_prot_commit
>>>>>> mm: Batch around can_change_pte_writable()
>>>>>> mm: Optimize mprotect() through PTE-batching
>>>>>>
>>>>>> arch/arm64/include/asm/pgtable.h | 10 ++
>>>>>> arch/arm64/mm/mmu.c | 21 +++-
>>>>>> include/linux/mm.h | 4 +-
>>>>>> include/linux/pgtable.h | 42 ++++++++
>>>>>> mm/gup.c | 2 +-
>>>>>> mm/huge_memory.c | 4 +-
>>>>>> mm/memory.c | 6 +-
>>>>>> mm/mprotect.c | 165 +++++++++++++++++++
>>>>>> +-----------
>>>>>> mm/pgtable-generic.c | 16 ++-
>>>>>> 9 files changed, 198 insertions(+), 72 deletions(-)
>>>>>>
>>>>>
>>>>
>>
>
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