Messages in this thread | | | From | David Hildenbrand <> | Subject | Re: [PATCH v7 1/1] mm/page_alloc.c: refactor initialization of struct page for holes in memory layout | Date | Thu, 25 Feb 2021 16:59:06 +0100 |
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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? This might worth documenting - also, you might want to take some of the original comment the accompanied this code.
You should also document (in the patch description?) that node/zone spans are not properly handled yet for such hole pfns and that this might require care in the future.
I played a little with weird setups and expected the memap state using page-types (well, I can't inspect the node/zone that way but at least have a look if the memmap was initialized). No surprises.
-- Thanks,
David / dhildenb
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