On Tue, 10 May 2022 13:32:20 -0700 Yang Shi <shy828301@xxxxxxxxx> wrote:
> The hugepage_vma_check() could be reused by khugepaged_enter() and
> khugepaged_enter_vma_merge(), but it is static in khugepaged.c.
> Make it non-static and declare it in khugepaged.h.
>
> ..
>
> @@ -508,20 +508,13 @@ void __khugepaged_enter(struct mm_struct *mm)
> void khugepaged_enter_vma_merge(struct vm_area_struct *vma,
> unsigned long vm_flags)
> {
> - unsigned long hstart, hend;
> -
> - /*
> - * khugepaged only supports read-only files for non-shmem files.
> - * khugepaged does not yet work on special mappings. And
> - * file-private shmem THP is not supported.
> - */
> - if (!hugepage_vma_check(vma, vm_flags))
> - return;
> -
> - hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
> - hend = vma->vm_end & HPAGE_PMD_MASK;
> - if (hstart < hend)
> - khugepaged_enter(vma, vm_flags);
> + if (!test_bit(MMF_VM_HUGEPAGE, &vma->vm_mm->flags) &&
> + khugepaged_enabled() &&
> + (((vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK) <
> + (vma->vm_end & HPAGE_PMD_MASK))) {
Reviewing these bounds-checking tests is so hard :( Can we simplify?
> + if (hugepage_vma_check(vma, vm_flags))
> + __khugepaged_enter(vma->vm_mm);
> + }
> }
void khugepaged_enter_vma(struct vm_area_struct *vma,
unsigned long vm_flags)
{
if (test_bit(MMF_VM_HUGEPAGE, &vma->vm_mm->flags))
return;
if (!khugepaged_enabled())
return;
if (round_up(vma->vm_start, HPAGE_PMD_SIZE) >=
(vma->vm_end & HPAGE_PMD_MASK))
return; /* vma is too small */
if (!hugepage_vma_check(vma, vm_flags))
return;
__khugepaged_enter(vma->vm_mm);
}
Also, it might be slightly faster to have checked MMF_VM_HUGEPAGE
before khugepaged_enabled(), but it looks odd. And it might be slower,
too - more pointer chasing.
I wish someone would document hugepage_vma_check().
