On 14 Oct 2024, at 6:24, Baolin Wang wrote:
> Khugepaged already supports collapsing file large folios (including shmem mTHP)
> by commit 7de856ffd007 ("mm: khugepaged: support shmem mTHP collapse"), and the
> control parameters in khugepaged: 'khugepaged_max_ptes_swap' and 'khugepaged_max_ptes_none',
> still compare based on PTE granularity to determine whether a file collapse is
> needed. However, the statistics for 'present' and 'swap' in hpage_collapse_scan_file()
> do not take into account the large folios, which may lead to incorrect judgments
> regarding the khugepaged_max_ptes_swap/none parameters, resulting in unnecessary
> file collapses.
>
> To fix this issue, take into account the large folios' statistics for 'present'
> and 'swap' variables in the hpage_collapse_scan_file().
>
> Fixes: 7de856ffd007 ("mm: khugepaged: support shmem mTHP collapse")
> Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
> ---
> mm/khugepaged.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index ba28ba09fe89..6f8d46d107b4 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -2267,7 +2267,7 @@ static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr,
> continue;
>
> if (xa_is_value(folio)) {
> - ++swap;
> + swap += 1 << xas_get_order(&xas);
xas_get_order() scans xarry sibling entries to get the order. You probably
can call xas_get_order() outside the loop after rcu_read_lock() and use
the result inside, since xas order is not changed, right?
> if (cc->is_khugepaged &&
> swap > khugepaged_max_ptes_swap) {
> result = SCAN_EXCEED_SWAP_PTE;
> @@ -2314,7 +2314,7 @@ static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr,
> * is just too costly...
> */
>
> - present++;
> + present += folio_nr_pages(folio);
>
> if (need_resched()) {
> xas_pause(&xas);
> --
> 2.39.3
Otherwise, LGTM. Thanks. Reviewed-by: Zi Yan <ziy@xxxxxxxxxx>
--
Best Regards,
Yan, Zi
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