[PATCH 0/7] Optimize mprotect for large folios

[Lance Yang]

I'm hitting the following compilation errors after applying this patch
series:

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(-)
>