On 25.02.21 18:06, Mike Rapoport wrote:
On Thu, Feb 25, 2021 at 04:59:06PM +0100, David Hildenbrand wrote:
On 24.02.21 16:39, Mike Rapoport wrote:
From: Mike Rapoport rppt@linux.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.
Before commit 73a6e474cb37 ("mm: memmap_init: iterate over memblock regions rather that check each PFN") the holes inside a zone were re-initialized during memmap_init() and got their zone/node links right. However, after that commit nothing updates the struct pages representing such holes.
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.
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.
With this change the pages for holes inside a zone will get proper zone/node links and the pages that are not spanned by any node will get links to the adjacent zone/node.
Fixes: 73a6e474cb37 ("mm: memmap_init: iterate over memblock regions rather that check each PFN") Signed-off-by: Mike Rapoport rppt@linux.ibm.com Reported-by: Qian Cai cai@lca.pw Reported-by: Andrea Arcangeli aarcange@redhat.com Reviewed-by: Baoquan He bhe@redhat.com
mm/page_alloc.c | 147 +++++++++++++++++++++--------------------------- 1 file changed, 64 insertions(+), 83 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 3e93f8b29bae..a11a9acde708 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -6280,12 +6280,60 @@ 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);
- static unsigned long hole_pfn = 0; unsigned long start_pfn, end_pfn;
- 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);
@@ -6295,7 +6343,23 @@ void __meminit __weak memmap_init_zone(struct zone *zone) 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;+#ifdef CONFIG_SPARSEMEM
- end_pfn = round_up(zone_end_pfn, PAGES_PER_SECTION);
- if (hole_pfn < end_pfn)
pgcnt += init_unavailable_range(hole_pfn, end_pfn,zone_id, nid);We might still double-initialize PFNs when two zones overlap within a section, correct?
You mean that a section crosses zones boundary? I don't think it's that important.
This might worth documenting - also, you might want to take some of the original comment the accompanied this code.
The original comment was not exactly right, I believe the comment above init_unavailable_range() better describes what's going on there.
Ah, okay - as long as it's documented I'm happy :)