+ linuxppc-...@lists.ozlabs.org
+ linux-i...@vger.kernel.org
On 4/12/21 9:18 AM, Anshuman Khandual wrote:
> pageblock_order must always be less than MAX_ORDER, otherwise it might lead
> to an warning during boot. A similar problem got fixed on arm64 platform
> with the commit 79cc2ed5a716 ("arm64/mm: Drop THP conditionality from
> FORCE_MAX_ZONEORDER"). Assert the above condition before HUGETLB_PAGE_ORDER
> gets assigned as pageblock_order. This will help detect the problem earlier
> on platforms where HUGETLB_PAGE_SIZE_VARIABLE is enabled.
>
> Cc: David Hildenbrand <da...@redhat.com>
> Cc: Andrew Morton <a...@linux-foundation.org>
> Cc: linux...@kvack.org
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: Anshuman Khandual <anshuman.khand...@arm.com>
> ---
> Changes in V2:
>
> - Changed WARN_ON() to BUILD_BUG_ON() per David
>
> Changes in V1:
>
> https://patchwork.kernel.org/project/linux-mm/patch/1617947717-2424-1-git-send-email-anshuman.khand...@arm.com/
>
> mm/page_alloc.c | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index cfc72873961d..19283bff4bec 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -6875,10 +6875,17 @@ void __init set_pageblock_order(void)
> if (pageblock_order)
> return;
>
> - if (HPAGE_SHIFT > PAGE_SHIFT)
> + if (HPAGE_SHIFT > PAGE_SHIFT) {
> + /*
> + * pageblock_order must always be less than
> + * MAX_ORDER. So does HUGETLB_PAGE_ORDER if
> + * that is being assigned here.
> + */
> + BUILD_BUG_ON(HUGETLB_PAGE_ORDER >= MAX_ORDER);
Unfortunately the build test fails on both the platforms (powerpc and ia64)
which subscribe HUGETLB_PAGE_SIZE_VARIABLE and where this check would make
sense. I some how overlooked the cross compile build failure that actually
detected this problem.
But wondering why this assert is not holding true ? and how these platforms
do not see the warning during boot (or do they ?) at mm/vmscan.c:1092 like
arm64 did.
static int __fragmentation_index(unsigned int order, struct contig_page_info
*info)
{
unsigned long requested = 1UL << order;
if (WARN_ON_ONCE(order >= MAX_ORDER))
return 0;
....
Can pageblock_order really exceed MAX_ORDER - 1 ?
> order = HUGETLB_PAGE_ORDER;
> - else
> + } else {
> order = MAX_ORDER - 1;
> + }
>
> /*
> * Assume the largest contiguous order of interest is a huge page.
>
