Re: [PATCH 0/7] Optimize mprotect for large folios

[Dev Jain <dev.jain@arm.com>]

On 28/04/25 7:01 pm, Lance Yang wrote:
> I'm hitting the following compilation errors after applying this patch
> series:

Not sure why is that. I cherry-picked my commits onto 
6ebffe676fcf8d259e3fb5d5fbf1a8227f22182c and the kernel builds for me.
Let me send a v2 rebased onto this.

> 
> 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);
>        |                 ^~~~~~~~~~~~~~~~~~~~~~~
> 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: *** [Makefile:248: __sub-make] Error 2
> 
> Based on:
> 
> mm-unstable b18dec6a6ad3d051dadc3c16fb838e4abddf8d3c ("mm/numa: remove 
> unnecessary local variable in alloc_node_data()")
> 
> 
> Thanks,
> Lance
> 
> 
> 
> On 2025/4/28 20:04, 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 276% performance improvement.
>>
>> 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                    | 163 +++++++++++++++++++++----------
>>   mm/pgtable-generic.c             |  16 ++-
>>   9 files changed, 198 insertions(+), 70 deletions(-)
>>
> 
>