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

[Mike Rapoport <rppt@kernel.org>]

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  |
+--------+--------+- ... -+          +--------+- ... -+--------+---------+


> 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?
 
-- 
Sincerely yours,
Mike.
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