mm/hugetlb: pass correct order_per_bit to cma_declare_contiguous_nid

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>

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 228c886c46c1954bbdda2b3e339989f6865f4552..5dc3f5ea3a2ef21874d6d6e3d8dfe77e6fd9f81e 100644 (file)
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -7794,9 +7794,9 @@ void __init hugetlb_cma_reserve(int order)
                 * 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);