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Message-ID: <5dccbc93-f260-7f14-23bc-6dee2dff6c13@redhat.com>
Date: Fri, 12 Feb 2021 10:55:09 +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 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
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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