Re: arm32: panic in move_freepages (Was [PATCH v2 0/4] arm64: drop pfn_valid_within() and simplify pfn_valid())

From: Kefeng Wang
Date: Wed May 12 2021 - 23:44:16 EST



On 2021/5/12 16:26, Mike Rapoport wrote:
On Wed, May 12, 2021 at 11:08:14AM +0800, Kefeng Wang wrote:

On 2021/5/11 16:48, Mike Rapoport wrote:
On Mon, May 10, 2021 at 11:10:20AM +0800, Kefeng Wang wrote:

The memory is not continuous, see MEMBLOCK:
memory size = 0x4c0fffff reserved size = 0x027ef058
memory.cnt = 0xa
memory[0x0] [0x80a00000-0x855fffff], 0x04c00000 bytes flags: 0x0
memory[0x1] [0x86a00000-0x87dfffff], 0x01400000 bytes flags: 0x0
memory[0x2] [0x8bd00000-0x8c4fffff], 0x00800000 bytes flags: 0x0
memory[0x3] [0x8e300000-0x8ecfffff], 0x00a00000 bytes flags: 0x0
memory[0x4] [0x90d00000-0xbfffffff], 0x2f300000 bytes flags: 0x0
memory[0x5] [0xcc000000-0xdc9fffff], 0x10a00000 bytes flags: 0x0
memory[0x6] [0xde700000-0xde9fffff], 0x00300000 bytes flags: 0x0
...

The pfn_range [0xde600,0xde700] => addr_range [0xde600000,0xde700000]
is not available memory, and we won't create memmap , so with or without
your patch, we can't see the range in free_memmap(), right?

This is not available memory and we won't see the reange in free_memmap(),
but we still should create memmap for it and that's what my patch tried to
do.

There are a lot of places in core mm that operate on pageblocks and
free_unused_memmap() should make sure that any pageblock has a valid memory
map.

Currently, that's not the case when SPARSEMEM=y and my patch tried to fix
it.

Can you please send log with my patch applied and with the printing of
ranges that are freed in free_unused_memmap() you've used in previous
mails?

with your patch[1] and debug print in free_memmap,
----> free_memmap, start_pfn = 85800, 85800000 end_pfn = 86800, 86800000
----> free_memmap, start_pfn = 8c800, 8c800000 end_pfn = 8e000, 8e000000
----> free_memmap, start_pfn = 8f000, 8f000000 end_pfn = 90000, 90000000
----> free_memmap, start_pfn = dcc00, dcc00000 end_pfn = de400, de400000
----> free_memmap, start_pfn = dec00, dec00000 end_pfn = e0000, e0000000
----> free_memmap, start_pfn = e0c00, e0c00000 end_pfn = e4000, e4000000
----> free_memmap, start_pfn = f7000, f7000000 end_pfn = f8000, f8000000

It seems that freeing of the memory map is suboptimal still because that
code was not designed for memory layout that has more holes than Swiss
cheese.

Still, the range [0xde600,0xde700] is not freed and there should be struct
pages for this range.

Can you add

dump_page(pfn_to_page(0xde600), "");

say, in the end of memblock_free_all()?

The range [0xde600,0xde700] is not memory, so it won't create struct page
for it when sparse_init?

sparse_init() indeed does not create memory map for unpopulated memory, but
it has pretty coarse granularity, i.e. 64M in your configuration. A hole
should be at least 64M in order to skip allocation of the memory map for
it.

For example, your memory layout has a hole of 192M at pfn 0xc0000 and this
hole won't have the memory map.

However the hole 0xdca00 - 0xde70 will still have a memory map in the
section that covers 0xdc000 - 0xe0000.

I've tried outline this in a sketch below, hope it helps.

Memory:
c0000 cc000 dca00
--------------------------+ +--------------------------+ +----+
memory bank |<- hole ->| memory bank | | mb |
--------------------------+ +--------------------------+ +----+
de700 dea00

Memory map:

b0000 b4000 c0000 cc000 d0000 d8000 dc000
+--------+--------+- ... -+ +--------+- ... -+--------+---------+
| memmap | memmap | ... |<- hole ->| memmap | ... | memmap | memmap |
+--------+--------+- ... -+ +--------+- ... -+--------+---------+


Thanks for the sketch, it is more clear,

After apply patch[1], the dump_page log,

page:ef3cc000 is uninitialized and poisoned
raw: ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff
page dumped because:

This means that there is a memory map entry, and it got poisoned during the
initialization and never got reinitialized to sensible values, which would
be PageReserved() in this case.

I believe this was fixed by commit 0740a50b9baa ("mm/page_alloc.c: refactor
initialization of struct page for holes in memory layout") in the mainline
tree.

Can you backport it to your 5.10 tree and check if it helps?
Hi Mike, the 0740a50b9baa is already in 5.10, tags/v5.10.24~5

commit 4c84191cbc3eff49568d3c5cccb628fa382cf7fb
Author: Mike Rapoport <rppt@xxxxxxxxxx>
Date: Fri Mar 12 21:07:12 2021 -0800

mm/page_alloc.c: refactor initialization of struct page for holes in memory layout

commit 0740a50b9baa4472cfb12442df4b39e2712a64a4 upstream.

but check init_unavailable_range(), we need deal with the hole in the
range of one pageblock.

For our scene, pageblock range: 0xde600,0xde7ff, but the available pfn begin with 0xde700.

If pfn(eg, 0xde600) is not valid, the step in init_unavailable_range is
pageblock_nr_pages, and ALIGN_DOWN(pfn, pageblock_nr_pages) from 0xde600
to 0xde700 is same, so the page range for pfn [0xde600,0xde700] won't be
initialized.

After add the following patch, the oom test could passed,

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index aaa1655cf682..0c7e04f86f9f 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6484,13 +6484,14 @@ static u64 __meminit init_unavailable_range(unsigned long spfn,
unsigned long epfn,
int zone, int node)
{
- unsigned long pfn;
+ unsigned long pfn, pfn_down;
+ unsigned long epfn_down = ALIGN_DOWN(epfn, pageblock_nr_pages);
u64 pgcnt = 0;

for (pfn = spfn; pfn < epfn; pfn++) {
- if (!pfn_valid(ALIGN_DOWN(pfn, pageblock_nr_pages))) {
- pfn = ALIGN_DOWN(pfn, pageblock_nr_pages)
- + pageblock_nr_pages - 1;
+ pfn_down = ALIGN_DOWN(pfn, pageblock_nr_pages);
+ if (!pfn_valid(pfn_down) && pfn_down != epfn_down) {
+ pfn = pfn_down + pageblock_nr_pages - 1;
continue;
}
__init_single_page(pfn_to_page(pfn), pfn, zone, node);


Before:
On node 0 totalpages: 311551
Normal zone: 1230 pages used for memmap
Normal zone: 0 pages reserved
Normal zone: 157440 pages, LIFO batch:31
Normal zone: 16384 pages in unavailable ranges
HighMem zone: 154111 pages, LIFO batch:31
HighMem zone: 1 pages in unavailable ranges

page:ef3cc000 is uninitialized and poisoned
raw: ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff

After:
On node 0 totalpages: 311551
Normal zone: 1230 pages used for memmap
Normal zone: 0 pages reserved
Normal zone: 157440 pages, LIFO batch:31
Normal zone: 17152 pages in unavailable ranges
HighMem zone: 154111 pages, LIFO batch:31
HighMem zone: 513 pages in unavailable ranges
...
page:(ptrval) refcount:1 mapcount:0 mapping:00000000 index:0x0 pfn:0xde600
flags: 0xdd001000(reserved)
raw: dd001000 ef3cc004 ef3cc004 00000000 00000000 00000000 ffffffff 00000001