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    Subject[PATCH 04/26] mm/arm: Use general page fault accounting
    Date
    Use the general page fault accounting by passing regs into handle_mm_fault().
    It naturally solve the issue of multiple page fault accounting when page fault
    retry happened. To do this, we need to pass the pt_regs pointer into
    __do_page_fault().

    Fix PERF_COUNT_SW_PAGE_FAULTS perf event manually for page fault retries, by
    moving it before taking mmap_sem.

    CC: Russell King <linux@armlinux.org.uk>
    CC: Will Deacon <will@kernel.org>
    CC: linux-arm-kernel@lists.infradead.org
    Signed-off-by: Peter Xu <peterx@redhat.com>
    ---
    arch/arm/mm/fault.c | 25 ++++++-------------------
    1 file changed, 6 insertions(+), 19 deletions(-)

    diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c
    index 0d6be0f4f27c..8530befee012 100644
    --- a/arch/arm/mm/fault.c
    +++ b/arch/arm/mm/fault.c
    @@ -201,7 +201,8 @@ static inline bool access_error(unsigned int fsr, struct vm_area_struct *vma)

    static vm_fault_t __kprobes
    __do_page_fault(struct mm_struct *mm, unsigned long addr, unsigned int fsr,
    - unsigned int flags, struct task_struct *tsk)
    + unsigned int flags, struct task_struct *tsk,
    + struct pt_regs *regs)
    {
    struct vm_area_struct *vma;
    vm_fault_t fault;
    @@ -223,7 +224,7 @@ __do_page_fault(struct mm_struct *mm, unsigned long addr, unsigned int fsr,
    goto out;
    }

    - return handle_mm_fault(vma, addr & PAGE_MASK, flags, NULL);
    + return handle_mm_fault(vma, addr & PAGE_MASK, flags, regs);

    check_stack:
    /* Don't allow expansion below FIRST_USER_ADDRESS */
    @@ -265,6 +266,8 @@ do_page_fault(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
    if ((fsr & FSR_WRITE) && !(fsr & FSR_CM))
    flags |= FAULT_FLAG_WRITE;

    + perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, addr);
    +
    /*
    * As per x86, we may deadlock here. However, since the kernel only
    * validly references user space from well defined areas of the code,
    @@ -289,7 +292,7 @@ do_page_fault(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
    #endif
    }

    - fault = __do_page_fault(mm, addr, fsr, flags, tsk);
    + fault = __do_page_fault(mm, addr, fsr, flags, tsk, regs);

    /* If we need to retry but a fatal signal is pending, handle the
    * signal first. We do not need to release the mmap_sem because
    @@ -301,23 +304,7 @@ do_page_fault(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
    return 0;
    }

    - /*
    - * Major/minor page fault accounting is only done on the
    - * initial attempt. If we go through a retry, it is extremely
    - * likely that the page will be found in page cache at that point.
    - */
    -
    - perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, addr);
    if (!(fault & VM_FAULT_ERROR) && flags & FAULT_FLAG_ALLOW_RETRY) {
    - if (fault & VM_FAULT_MAJOR) {
    - tsk->maj_flt++;
    - perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1,
    - regs, addr);
    - } else {
    - tsk->min_flt++;
    - perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1,
    - regs, addr);
    - }
    if (fault & VM_FAULT_RETRY) {
    flags |= FAULT_FLAG_TRIED;
    goto retry;
    --
    2.26.2
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