The following warning gets triggered while trying to boot a 64K page size
without THP config kernel on arm64 platform.
WARNING: CPU: 5 PID: 124 at mm/vmstat.c:1080 __fragmentation_index+0xa4/0xc0
Modules linked in:
CPU: 5 PID: 124 Comm: kswapd0 Not tainted 5.11.0-rc6-00004-ga0ea7d62002 #159
Hardware name: linux,dummy-virt (DT)
[ 8.810673] pstate: 20400005 (nzCv daif +PAN -UAO -TCO BTYPE=--)
[ 8.811732] pc : __fragmentation_index+0xa4/0xc0
[ 8.812555] lr : fragmentation_index+0xf8/0x138
[ 8.813360] sp : ffff0000864079b0
[ 8.813958] x29: ffff0000864079b0 x28: 0000000000000372
[ 8.814901] x27: 0000000000007682 x26: ffff8000135b3948
[ 8.815847] x25: 1fffe00010c80f48 x24: 0000000000000000
[ 8.816805] x23: 0000000000000000 x22: 000000000000000d
[ 8.817764] x21: 0000000000000030 x20: ffff0005ffcb4d58
[ 8.818712] x19: 000000000000000b x18: 0000000000000000
[ 8.819656] x17: 0000000000000000 x16: 0000000000000000
[ 8.820613] x15: 0000000000000000 x14: ffff8000114c6258
[ 8.821560] x13: ffff6000bff969ba x12: 1fffe000bff969b9
[ 8.822514] x11: 1fffe000bff969b9 x10: ffff6000bff969b9
[ 8.823461] x9 : dfff800000000000 x8 : ffff0005ffcb4dcf
[ 8.824415] x7 : 0000000000000001 x6 : 0000000041b58ab3
[ 8.825359] x5 : ffff600010c80f48 x4 : dfff800000000000
[ 8.826313] x3 : ffff8000102be670 x2 : 0000000000000007
[ 8.827259] x1 : ffff000086407a60 x0 : 000000000000000d
[ 8.828218] Call trace:
[ 8.828667] __fragmentation_index+0xa4/0xc0
[ 8.829436] fragmentation_index+0xf8/0x138
[ 8.830194] compaction_suitable+0x98/0xb8
[ 8.830934] wakeup_kcompactd+0xdc/0x128
[ 8.831640] balance_pgdat+0x71c/0x7a0
[ 8.832327] kswapd+0x31c/0x520
[ 8.832902] kthread+0x224/0x230
[ 8.833491] ret_from_fork+0x10/0x30
[ 8.834150] ---[ end trace 472836f79c15516b ]---
This warning comes from __fragmentation_index() when the requested order
is greater than MAX_ORDER.
static int __fragmentation_index(unsigned int order,
struct contig_page_info *info)
{
unsigned long requested = 1UL << order;
if (WARN_ON_ONCE(order >= MAX_ORDER)) <===== Triggered here
return 0;
Digging it further reveals that pageblock_order has been assigned a value
which is greater than MAX_ORDER failing the above check. But why this
happened ? Because HUGETLB_PAGE_ORDER for the given config on arm64 is
greater than MAX_ORDER.
The solution involves enabling HUGETLB_PAGE_SIZE_VARIABLE which would make
pageblock_order a variable instead of constant HUGETLB_PAGE_ORDER. But that
change alone also did not really work as pageblock_order still got assigned
as HUGETLB_PAGE_ORDER in set_pageblock_order(). HUGETLB_PAGE_ORDER needs to
be less than MAX_ORDER for its appropriateness as pageblock_order otherwise
just fallback to MAX_ORDER - 1 as before. While here it also fixes a build
problem via type casting MAX_ORDER in rmem_cma_setup().
This series applies in v5.11-rc6 and has been slightly tested on arm64. But
looking for some early feedbacks particularly with respect to concerns in
subscribing HUGETLB_PAGE_SIZE_VARIABLE on a platform where the hugetlb page
size is config dependent but not really a runtime variable. Even though it
appears that HUGETLB_PAGE_SIZE_VARIABLE is used only while computing the
pageblock_order, could there be other implications ?
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Cc: Robin Murphy <robin.murphy@xxxxxxx>
Cc: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
Cc: iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx
Cc: linux-mm@xxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Anshuman Khandual (3):
mm/page_alloc: Fix pageblock_order when HUGETLB_PAGE_ORDER >= MAX_ORDER
arm64/hugetlb: Enable HUGETLB_PAGE_SIZE_VARIABLE
dma-contiguous: Type cast MAX_ORDER as unsigned int
arch/arm64/Kconfig | 4 ++++
kernel/dma/contiguous.c | 2 +-
mm/page_alloc.c | 2 +-
3 files changed, 6 insertions(+), 2 deletions(-)
--
2.20.1
