On Sun, Apr 4, 2021 at 8:33 AM <yanfei.xu@xxxxxxxxxxxxx> wrote:
>
> From: Yanfei Xu <yanfei.xu@xxxxxxxxxxxxx>
>
> We could check MMF_DISABLE_THP ahead of iterating over all of vma.
> Otherwise if some mm_struct contain a large number of vma, there will
> be amounts meaningless cpu cycles cost.
>
> BTW, drop an unnecessary cond_resched(), because there is a another
> cond_resched() followed it and no consumed invocation between them.
>
> Signed-off-by: Yanfei Xu <yanfei.xu@xxxxxxxxxxxxx>
> ---
> mm/khugepaged.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 2efe1d0c92ed..c293ec4a94ea 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -2094,6 +2094,8 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages,
> */
> if (unlikely(!mmap_read_trylock(mm)))
> goto breakouterloop_mmap_lock;
> + if (test_bit(MMF_DISABLE_THP, &mm->flags))
> + goto breakouterloop_mmap_lock;
It is fine to check this flag. But mmap_lock has been acquired so you
should jump to breakouterloop.
> if (likely(!khugepaged_test_exit(mm)))
> vma = find_vma(mm, khugepaged_scan.address);
>
> @@ -2101,7 +2103,6 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages,
> for (; vma; vma = vma->vm_next) {
> unsigned long hstart, hend;
>
> - cond_resched();
I don't have a strong opinion for removing this cond_resched(). But
IIUC khugepaged is a best effort job there is no harm to keep it IMHO.
> if (unlikely(khugepaged_test_exit(mm))) {
> progress++;
> break;
> --
> 2.27.0
>
>
