On Tue, Jul 11, 2023 at 1:20 PM Matthew Wilcox (Oracle)
<willy@xxxxxxxxxxxxx> wrote:
>
> Handle a little more of the page fault path outside the mmap sem.
> The hugetlb path doesn't need to check whether the VMA is anonymous;
> the VM_HUGETLB flag is only set on hugetlbfs VMAs. There should be no
> performance change from the previous commit; this is simply a step to
> ease bisection of any problems.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Reviewed-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
> ---
> mm/hugetlb.c | 6 ++++++
> mm/memory.c | 18 +++++++++---------
> 2 files changed, 15 insertions(+), 9 deletions(-)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index e4a28ce0667f..109e1ff92bc8 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -6063,6 +6063,12 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
> int need_wait_lock = 0;
> unsigned long haddr = address & huge_page_mask(h);
>
> + /* TODO: Handle faults under the VMA lock */
> + if (flags & FAULT_FLAG_VMA_LOCK) {
> + vma_end_read(vma);
> + return VM_FAULT_RETRY;
> + }
> +
> /*
> * Serialize hugepage allocation and instantiation, so that we don't
> * get spurious allocation failures if two CPUs race to instantiate
> diff --git a/mm/memory.c b/mm/memory.c
> index f2dcc695f54e..6eda5c5f2069 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -4998,10 +4998,10 @@ static vm_fault_t handle_pte_fault(struct vm_fault *vmf)
> }
>
> /*
> - * By the time we get here, we already hold the mm semaphore
> - *
> - * The mmap_lock may have been released depending on flags and our
> - * return value. See filemap_fault() and __folio_lock_or_retry().
> + * On entry, we hold either the VMA lock or the mmap_lock
> + * (FAULT_FLAG_VMA_LOCK tells you which). If VM_FAULT_RETRY is set in
> + * the result, the mmap_lock is not held on exit. See filemap_fault()
> + * and __folio_lock_or_retry().
> */
> static vm_fault_t __handle_mm_fault(struct vm_area_struct *vma,
> unsigned long address, unsigned int flags)
> @@ -5020,6 +5020,11 @@ static vm_fault_t __handle_mm_fault(struct vm_area_struct *vma,
> p4d_t *p4d;
> vm_fault_t ret;
>
> + if ((flags & FAULT_FLAG_VMA_LOCK) && !vma_is_anonymous(vma)) {
> + vma_end_read(vma);
> + return VM_FAULT_RETRY;
> + }
> +
> pgd = pgd_offset(mm, address);
> p4d = p4d_alloc(mm, pgd, address);
> if (!p4d)
> @@ -5247,11 +5252,6 @@ vm_fault_t handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
> goto out;
> }
>
> - if ((flags & FAULT_FLAG_VMA_LOCK) && !vma_is_anonymous(vma)) {
> - vma_end_read(vma);
> - return VM_FAULT_RETRY;
> - }
> -
> /*
> * Enable the memcg OOM handling for faults triggered in user
> * space. Kernel faults are handled more gracefully.
> --
> 2.39.2
>
