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Date: Fri, 12 Feb 2021 10:56:19 +0100
From: David Hildenbrand <david@...hat.com>
To: Mike Rapoport <rppt@...nel.org>,
Andrew Morton <akpm@...ux-foundation.org>
Cc: Andrea Arcangeli <aarcange@...hat.com>,
Baoquan He <bhe@...hat.com>, Borislav Petkov <bp@...en8.de>,
Chris Wilson <chris@...is-wilson.co.uk>,
"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Łukasz Majczak <lma@...ihalf.com>,
Mel Gorman <mgorman@...e.de>, Michal Hocko <mhocko@...nel.org>,
Mike Rapoport <rppt@...ux.ibm.com>, Qian Cai <cai@....pw>,
"Sarvela, Tomi P" <tomi.p.sarvela@...el.com>,
Thomas Gleixner <tglx@...utronix.de>,
Vlastimil Babka <vbabka@...e.cz>, linux-kernel@...r.kernel.org,
linux-mm@...ck.org, stable@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH v5 1/1] mm: refactor initialization of struct page for
holes in memory layout
On 12.02.21 10:55, David Hildenbrand wrote:
> On 08.02.21 12:08, Mike Rapoport wrote:
>> From: Mike Rapoport <rppt@...ux.ibm.com>
>>
>> There could be struct pages that are not backed by actual physical memory.
>> This can happen when the actual memory bank is not a multiple of
>> SECTION_SIZE or when an architecture does not register memory holes
>> reserved by the firmware as memblock.memory.
>>
>> Such pages are currently initialized using init_unavailable_mem() function
>> that iterates through PFNs in holes in memblock.memory and if there is a
>> struct page corresponding to a PFN, the fields of this page are set to
>> default values and it is marked as Reserved.
>>
>> init_unavailable_mem() does not take into account zone and node the page
>> belongs to and sets both zone and node links in struct page to zero.
>>
>> On a system that has firmware reserved holes in a zone above ZONE_DMA, for
>> instance in a configuration below:
>>
>> # grep -A1 E820 /proc/iomem
>> 7a17b000-7a216fff : Unknown E820 type
>> 7a217000-7bffffff : System RAM
>>
>> unset zone link in struct page will trigger
>>
>> VM_BUG_ON_PAGE(!zone_spans_pfn(page_zone(page), pfn), page);
>>
>> because there are pages in both ZONE_DMA32 and ZONE_DMA (unset zone link
>> in struct page) in the same pageblock.
>>
>> Moreover, it is possible that the lowest node and zone start is not aligned
>> to the section boundarie, for example on x86:
>>
>> [ 0.078898] Zone ranges:
>> [ 0.078899] DMA [mem 0x0000000000001000-0x0000000000ffffff]
>> ...
>> [ 0.078910] Early memory node ranges
>> [ 0.078912] node 0: [mem 0x0000000000001000-0x000000000009cfff]
>> [ 0.078913] node 0: [mem 0x0000000000100000-0x000000003fffffff]
>>
>> and thus with SPARSEMEM memory model the beginning of the memory map will
>> have struct pages that are not spanned by any node and zone.
>>
>> Update detection of node boundaries in get_pfn_range_for_nid() so that the
>> node range will be expanded to cover memory map section. Since zone spans
>> are derived from the node span, there always will be a zone that covers the
>> part of the memory map with unavailable pages.
>>
>> Interleave initialization of the unavailable pages with the normal
>> initialization of memory map, so that zone and node information will be
>> properly set on struct pages that are not backed by the actual memory.
>>
>> 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>
>> Cc: Baoquan He <bhe@...hat.com>
>> Cc: David Hildenbrand <david@...hat.com>
>> Cc: Mel Gorman <mgorman@...e.de>
>> Cc: Michal Hocko <mhocko@...nel.org>
>> Cc: Qian Cai <cai@....pw>
>> Cc: Vlastimil Babka <vbabka@...e.cz>
>> ---
>> mm/page_alloc.c | 160 +++++++++++++++++++++++-------------------------
>> 1 file changed, 75 insertions(+), 85 deletions(-)
>>
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 6446778cbc6b..1c3f7521028f 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -6257,22 +6257,84 @@ static void __meminit zone_init_free_lists(struct zone *zone)
>> }
>> }
>>
>> +#if !defined(CONFIG_FLAT_NODE_MEM_MAP)
>> +/*
>> + * Only struct pages that correspond to ranges defined by memblock.memory
>> + * are zeroed and initialized by going through __init_single_page() during
>> + * memmap_init_zone().
>> + *
>> + * But, there could be struct pages that correspond to holes in
>> + * memblock.memory. This can happen because of the following reasons:
>> + * - phyiscal memory bank size is not necessarily the exact multiple of the
>> + * arbitrary section size
>> + * - early reserved memory may not be listed in memblock.memory
>> + * - memory layouts defined with memmap= kernel parameter may not align
>> + * nicely with memmap sections
>> + *
>> + * Explicitly initialize those struct pages so that:
>> + * - PG_Reserved is set
>> + * - zone and node links point to zone and node that span the page
>> + */
>> +static u64 __meminit init_unavailable_range(unsigned long spfn,
>> + unsigned long epfn,
>> + int zone, int node)
>> +{
>> + unsigned long pfn;
>> + 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;
>> + continue;
>> + }
>> + __init_single_page(pfn_to_page(pfn), pfn, zone, node);
>> + __SetPageReserved(pfn_to_page(pfn));
>> + pgcnt++;
>> + }
>> +
>> + return pgcnt;
>> +}
>> +#else
>> +static inline u64 init_unavailable_range(unsigned long spfn, unsigned long epfn,
>> + int zone, int node)
>> +{
>> + return 0;
>> +}
>> +#endif
>> +
>> void __meminit __weak memmap_init_zone(struct zone *zone)
>> {
>> unsigned long zone_start_pfn = zone->zone_start_pfn;
>> unsigned long zone_end_pfn = zone_start_pfn + zone->spanned_pages;
>> int i, nid = zone_to_nid(zone), zone_id = zone_idx(zone);
>> unsigned long start_pfn, end_pfn;
>> + unsigned long hole_pfn = 0;
>> + u64 pgcnt = 0;
>>
>> for_each_mem_pfn_range(i, nid, &start_pfn, &end_pfn, NULL) {
>> start_pfn = clamp(start_pfn, zone_start_pfn, zone_end_pfn);
>> end_pfn = clamp(end_pfn, zone_start_pfn, zone_end_pfn);
>> + hole_pfn = clamp(hole_pfn, zone_start_pfn, zone_end_pfn);
>>
>> if (end_pfn > start_pfn)
>> memmap_init_range(end_pfn - start_pfn, nid,
>> zone_id, start_pfn, zone_end_pfn,
>> MEMINIT_EARLY, NULL, MIGRATE_MOVABLE);
>> +
>> + if (hole_pfn < start_pfn)
>> + pgcnt += init_unavailable_range(hole_pfn, start_pfn,
>> + zone_id, nid);
>> + hole_pfn = end_pfn;
>> }
>> +
>> + if (hole_pfn < zone_end_pfn)
>> + pgcnt += init_unavailable_range(hole_pfn, zone_end_pfn,
>> + zone_id, nid);
>> +
>> + if (pgcnt)
>> + pr_info(" %s zone: %lld pages in unavailable ranges\n",
>> + zone->name, pgcnt);
>> }
>>
>> static int zone_batchsize(struct zone *zone)
>> @@ -6519,8 +6581,19 @@ void __init get_pfn_range_for_nid(unsigned int nid,
>> *end_pfn = max(*end_pfn, this_end_pfn);
>> }
>>
>> - if (*start_pfn == -1UL)
>> + if (*start_pfn == -1UL) {
>> *start_pfn = 0;
>> + return;
>> + }
>> +
>> +#ifdef CONFIG_SPARSEMEM
>> + /*
>> + * Sections in the memory map may not match actual populated
>> + * memory, extend the node span to cover the entire section.
>> + */
>> + *start_pfn = round_down(*start_pfn, PAGES_PER_SECTION);
>> + *end_pfn = round_up(*end_pfn, PAGES_PER_SECTION);
>
> Does that mean that we might create overlapping zones when one node
s/overlapping zones/overlapping nodes/
> starts in the middle of a section and the other one ends in the middle
> of a section?
>
> Could it be a problem? (e.g., would we have to look at neighboring nodes
> when making the decision to extend, and how far to extend?)
>
--
Thanks,
David / dhildenb
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