linux-kernel - Re: [PATCH v2 1/2] mm: memblock: enforce overlap of memory.memblock and memory.reserved

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Message-ID: <a512bd63-b171-3ed5-6996-2c99b6c9a226@redhat.com>
Date:   Mon, 14 Dec 2020 12:18:07 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Mike Rapoport <rppt@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Baoquan He <bhe@...hat.com>, Mel Gorman <mgorman@...e.de>,
        Michal Hocko <mhocko@...nel.org>,
        Mike Rapoport <rppt@...ux.ibm.com>, Qian Cai <cai@....pw>,
        Vlastimil Babka <vbabka@...e.cz>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, stable@...r.kernel.org,
        Dan Williams <dan.j.williams@...el.com>
Subject: Re: [PATCH v2 1/2] mm: memblock: enforce overlap of memory.memblock
 and memory.reserved

On 14.12.20 12:12, Mike Rapoport wrote:
> On Mon, Dec 14, 2020 at 11:11:35AM +0100, David Hildenbrand wrote:
>> On 09.12.20 22:43, Mike Rapoport wrote:
>>> From: Mike Rapoport <rppt@...ux.ibm.com>
>>>
>>> memblock does not require that the reserved memory ranges will be a subset
>>> of memblock.memory.
>>>
>>> As the result there maybe reserved pages that are not in the range of any
>>> zone or node because zone and node boundaries are detected based on
>>> memblock.memory and pages that only present in memblock.reserved are not
>>> taken into account during zone/node size detection.
>>>
>>> Make sure that all ranges in memblock.reserved are added to memblock.memory
>>> before calculating node and zone boundaries.
>>>
>>> Fixes: 73a6e474cb37 ("mm: memmap_init: iterate over memblock regions rather that check each PFN")
>>> Reported-by: Andrea Arcangeli <aarcange@...hat.com>
>>> Signed-off-by: Mike Rapoport <rppt@...ux.ibm.com>
>>> ---
>>>  include/linux/memblock.h |  1 +
>>>  mm/memblock.c            | 24 ++++++++++++++++++++++++
>>>  mm/page_alloc.c          |  7 +++++++
>>>  3 files changed, 32 insertions(+)
>>>
>>> diff --git a/include/linux/memblock.h b/include/linux/memblock.h
>>> index ef131255cedc..e64dae2dd1ce 100644
>>> --- a/include/linux/memblock.h
>>> +++ b/include/linux/memblock.h
>>> @@ -120,6 +120,7 @@ int memblock_clear_nomap(phys_addr_t base, phys_addr_t size);
>>>  unsigned long memblock_free_all(void);
>>>  void reset_node_managed_pages(pg_data_t *pgdat);
>>>  void reset_all_zones_managed_pages(void);
>>> +void memblock_enforce_memory_reserved_overlap(void);
>>>  
>>>  /* Low level functions */
>>>  void __next_mem_range(u64 *idx, int nid, enum memblock_flags flags,
>>> diff --git a/mm/memblock.c b/mm/memblock.c
>>> index b68ee86788af..9277aca642b2 100644
>>> --- a/mm/memblock.c
>>> +++ b/mm/memblock.c
>>> @@ -1857,6 +1857,30 @@ void __init_memblock memblock_trim_memory(phys_addr_t align)
>>>  	}
>>>  }
>>>  
>>> +/**
>>> + * memblock_enforce_memory_reserved_overlap - make sure every range in
>>> + * @memblock.reserved is covered by @memblock.memory
>>> + *
>>> + * The data in @memblock.memory is used to detect zone and node boundaries
>>> + * during initialization of the memory map and the page allocator. Make
>>> + * sure that every memory range present in @memblock.reserved is also added
>>> + * to @memblock.memory even if the architecture specific memory
>>> + * initialization failed to do so
>>> + */
>>> +void __init memblock_enforce_memory_reserved_overlap(void)
>>> +{
>>> +	phys_addr_t start, end;
>>> +	int nid;
>>> +	u64 i;
>>> +
>>> +	__for_each_mem_range(i, &memblock.reserved, &memblock.memory,
>>> +			     NUMA_NO_NODE, MEMBLOCK_NONE, &start, &end, &nid) {
>>> +		pr_warn("memblock: reserved range [%pa-%pa] is not in memory\n",
>>> +			&start, &end);
>>> +		memblock_add_node(start, (end - start), nid);
>>> +	}
>>> +}
>>> +
>>>  void __init_memblock memblock_set_current_limit(phys_addr_t limit)
>>>  {
>>>  	memblock.current_limit = limit;
>>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>>> index eaa227a479e4..dbc57dbbacd8 100644
>>> --- a/mm/page_alloc.c
>>> +++ b/mm/page_alloc.c
>>> @@ -7436,6 +7436,13 @@ void __init free_area_init(unsigned long *max_zone_pfn)
>>>  	memset(arch_zone_highest_possible_pfn, 0,
>>>  				sizeof(arch_zone_highest_possible_pfn));
>>>  
>>> +	/*
>>> +	 * Some architectures (e.g. x86) have reserved pages outside of
>>> +	 * memblock.memory. Make sure these pages are taken into account
>>> +	 * when detecting zone and node boundaries
>>> +	 */
>>> +	memblock_enforce_memory_reserved_overlap();
>>> +
>>>  	start_pfn = find_min_pfn_with_active_regions();
>>>  	descending = arch_has_descending_max_zone_pfns();
>>>  
>>>
>>
>> CCing Dan.
>>
>> This implies that any memory that is E820_TYPE_SOFT_RESERVED that was
>> reserved via memblock_reserve() will be added via memblock_add_node() as
>> well, resulting in all such memory getting a memmap allocated right when
>> booting up, right?
>>
>> IIRC, there are use cases where that is absolutely not desired.
> 
> Hmm, if this is the case we need entirely different solution to ensure
> that we don't have partial pageblocks in a zone and we have all the
> memory map initialized to a known state.
> 
>> Am I missing something? (@Dan?)
> 
> BTW, @Dan, why did you need to memblock_reserve(E820_TYPE_SOFT_RESERVED)
> without memblock_add()ing it?

I suspect to cover cases where it might partially span memory sections
(or even sub-sections). Maybe we should focus on initializing that part
only - meaning, not adding all memory to .memory but only !section
aligned pieces.


-- 
Thanks,

David / dhildenb