On 2/26/26 04:26, Nico Pache wrote:
> There are cases where, if an attempted collapse fails, all subsequent
> orders are guaranteed to also fail. Avoid these collapse attempts by
> bailing out early.
>
> Signed-off-by: Nico Pache <[email protected]>
> ---
> mm/khugepaged.c | 35 ++++++++++++++++++++++++++++++++++-
> 1 file changed, 34 insertions(+), 1 deletion(-)
>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 1c3711ed4513..388d3f2537e2 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -1492,9 +1492,42 @@ static int mthp_collapse(struct mm_struct *mm,
> unsigned long address,
> ret = collapse_huge_page(mm, collapse_address,
> referenced,
> unmapped, cc, mmap_locked,
> order);
> - if (ret == SCAN_SUCCEED) {
> +
> + switch (ret) {
> + /* Cases were we continue to next collapse candidate */
> + case SCAN_SUCCEED:
> collapsed += nr_pte_entries;
> + fallthrough;
> + case SCAN_PTE_MAPPED_HUGEPAGE:
> continue;
> + /* Cases were lower orders might still succeed */
> + case SCAN_LACK_REFERENCED_PAGE:
> + case SCAN_EXCEED_NONE_PTE:
> + case SCAN_EXCEED_SWAP_PTE:
> + case SCAN_EXCEED_SHARED_PTE:
> + case SCAN_PAGE_LOCK:
> + case SCAN_PAGE_COUNT:
> + case SCAN_PAGE_LRU:
> + case SCAN_PAGE_NULL:
> + case SCAN_DEL_PAGE_LRU:
> + case SCAN_PTE_NON_PRESENT:
> + case SCAN_PTE_UFFD_WP:
> + case SCAN_ALLOC_HUGE_PAGE_FAIL:
> + goto next_order;
> + /* Cases were no further collapse is possible */
> + case SCAN_CGROUP_CHARGE_FAIL:
> + case SCAN_COPY_MC:
> + case SCAN_ADDRESS_RANGE:
> + case SCAN_NO_PTE_TABLE:
> + case SCAN_ANY_PROCESS:
> + case SCAN_VMA_NULL:
> + case SCAN_VMA_CHECK:
> + case SCAN_SCAN_ABORT:
> + case SCAN_PAGE_ANON:
> + case SCAN_PMD_MAPPED:
> + case SCAN_FAIL:
> + default:
> + return collapsed;
> }
> }
>
LGTM, but I do wonder, given that you have the "default" case, why spell
out the ones that fall into the "default" category? I'd strip those
/* For all other cases no futher collapse is possible */
default:
return collapsed;
Acked-by: David Hildenbrand (Arm) <[email protected]>
--
Cheers,
David
