6.6-stable review patch. If anyone has any objections, please let me know.
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From: Frank van der Linden fvdl@google.com
commit 55d134a7b499c77e7cfd0ee41046f3c376e791e5 upstream.
The hugetlb_cma code passes 0 in the order_per_bit argument to cma_declare_contiguous_nid (the alignment, computed using the page order, is correctly passed in).
This causes a bit in the cma allocation bitmap to always represent a 4k page, making the bitmaps potentially very large, and slower.
It would create bitmaps that would be pretty big. E.g. for a 4k page size on x86, hugetlb_cma=64G would mean a bitmap size of (64G / 4k) / 8 == 2M. With HUGETLB_PAGE_ORDER as order_per_bit, as intended, this would be (64G / 2M) / 8 == 4k. So, that's quite a difference.
Also, this restricted the hugetlb_cma area to ((PAGE_SIZE << MAX_PAGE_ORDER) * 8) * PAGE_SIZE (e.g. 128G on x86) , since bitmap_alloc uses normal page allocation, and is thus restricted by MAX_PAGE_ORDER. Specifying anything about that would fail the CMA initialization.
So, correctly pass in the order instead.
Link: https://lkml.kernel.org/r/20240404162515.527802-2-fvdl@google.com Fixes: cf11e85fc08c ("mm: hugetlb: optionally allocate gigantic hugepages using cma") Signed-off-by: Frank van der Linden fvdl@google.com Acked-by: Roman Gushchin roman.gushchin@linux.dev Acked-by: David Hildenbrand david@redhat.com Cc: Marek Szyprowski m.szyprowski@samsung.com Cc: Muchun Song muchun.song@linux.dev Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- mm/hugetlb.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
--- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -7464,9 +7464,9 @@ void __init hugetlb_cma_reserve(int orde * huge page demotion. */ res = cma_declare_contiguous_nid(0, size, 0, - PAGE_SIZE << HUGETLB_PAGE_ORDER, - 0, false, name, - &hugetlb_cma[nid], nid); + PAGE_SIZE << HUGETLB_PAGE_ORDER, + HUGETLB_PAGE_ORDER, false, name, + &hugetlb_cma[nid], nid); if (res) { pr_warn("hugetlb_cma: reservation failed: err %d, node %d", res, nid);