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Message-ID: <05c3cd68-0d75-4682-a51c-59307e2b2e78@arm.com>
Date: Tue, 29 Apr 2025 14:32:59 +0530
From: Dev Jain <dev.jain@....com>
To: Lance Yang <lance.yang@...ux.dev>, akpm@...ux-foundation.org
Cc: 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, lorenzo.stoakes@...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 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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