Messages in this thread |  | | Subject | Re: [PATCH v6 1/1] mm/page_alloc.c: refactor initialization of struct page for holes in memory layout | From | David Hildenbrand <> | Date | Tue, 23 Feb 2021 10:49:44 +0100 |
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On 23.02.21 10:48, Mike Rapoport wrote: > On Tue, Feb 23, 2021 at 09:04:19AM +0100, David Hildenbrand wrote: >> On 22.02.21 11:57, 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. >> >> Does this include pages in the last section has handled by ... >> ... >>> - /* >>> - * Early sections always have a fully populated memmap for the whole >>> - * section - see pfn_valid(). If the last section has holes at the >>> - * end and that section is marked "online", the memmap will be >>> - * considered initialized. Make sure that memmap has a well defined >>> - * state. >>> - */ >>> - pgcnt += init_unavailable_range(PFN_DOWN(next), >>> - round_up(max_pfn, PAGES_PER_SECTION)); >>> - >> >> ^ this code? >> >> Or how is that case handled now? > > Hmm, now it's clamped to node_end_pfn/zone_end_pfn, so in your funny example with > > -object memory-backend-ram,id=bmem0,size=4160M \ > -object memory-backend-ram,id=bmem1,size=4032M \ > > this is not handled :( > > But it will be handled with this on top: > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 29bbd08b8e63..6c9b490f5a8b 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -6350,9 +6350,12 @@ void __meminit __weak memmap_init_zone(struct zone *zone) > hole_pfn = end_pfn; > } > > - if (hole_pfn < zone_end_pfn) > - pgcnt += init_unavailable_range(hole_pfn, zone_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); > +#endif > > if (pgcnt) > pr_info(" %s zone: %lld pages in unavailable ranges\n", >
Also, just wondering, will PFN 0 still get initialized?
-- Thanks,
David / dhildenb
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