Re: [PATCHv2 2/8] khugepaged: Do not stop collapse if less than half PTEs are referenced

[Yang Shi]

On 4/3/20 4:29 AM, Kirill A. Shutemov wrote:
> __collapse_huge_page_swapin() check number of referenced PTE to decide
> if the memory range is hot enough to justify swapin.
>
> The problem is that it stops collapse altogether if there's not enough
> referenced pages, not only swappingin.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Fixes: 0db501f7a34c ("mm, thp: convert from optimistic swapin collapsing to conservative")
> Reviewed-by: Zi Yan <ziy@xxxxxxxxxx>
> ---
>   mm/khugepaged.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)

Acked-by: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>

> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 99bab7e4d05b..14d7afc90786 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -905,7 +905,8 @@ static bool __collapse_huge_page_swapin(struct mm_struct *mm,
>   	/* we only decide to swapin, if there is enough young ptes */
>   	if (referenced < HPAGE_PMD_NR/2) {
>   		trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
> -		return false;
> +		/* Do not block collapse, only skip swapping in */
> +		return true;
>   	}
>   	vmf.pte = pte_offset_map(pmd, address);
>   	for (; vmf.address < address + HPAGE_PMD_NR*PAGE_SIZE;