A virtio-mem device wants to allocate memory from the memory region it manages in order to unplug it in the hypervisor - similar to a balloon driver. Also, it might want to plug previously unplugged (allocated) memory and give it back to Linux. alloc_contig_range() / free_contig_range() seem to be the perfect interface for this task. In contrast to existing balloon devices, a virtio-mem device operates on bigger chunks (e.g., 4MB) and only on physical memory it manages. It tracks which chunks (subblocks) are still plugged, so it can go ahead and try to alloc_contig_range()+unplug them on unplug request, or plug+free_contig_range() unplugged chunks on plug requests. A virtio-mem device will use alloc_contig_range() / free_contig_range() only on ranges that belong to the same node/zone in at least MAX(MAX_ORDER - 1, pageblock_order) order granularity - e.g., 4MB on x86-64. The virtio-mem device added that memory, so the memory exists and does not contain any holes. virtio-mem will only try to allocate on ZONE_NORMAL, never on ZONE_MOVABLE, just like when allocating gigantic pages (we don't put unmovable data into the movable zone). Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxx> Cc: Vlastimil Babka <vbabka@xxxxxxx> Cc: Oscar Salvador <osalvador@xxxxxxx> Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> Cc: Mike Rapoport <rppt@xxxxxxxxxxxxx> Cc: Dan Williams <dan.j.williams@xxxxxxxxx> Cc: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx> Cc: Pavel Tatashin <pavel.tatashin@xxxxxxxxxxxxx> Cc: Alexander Potapenko <glider@xxxxxxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxxx> # to export contig range allocator API Signed-off-by: David Hildenbrand <david@xxxxxxxxxx> --- mm/page_alloc.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 79e950d76ffc..8d7be3f33e26 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -8597,6 +8597,7 @@ int alloc_contig_range(unsigned long start, unsigned long end, pfn_max_align_up(end), migratetype); return ret; } +EXPORT_SYMBOL(alloc_contig_range); static int __alloc_contig_pages(unsigned long start_pfn, unsigned long nr_pages, gfp_t gfp_mask) @@ -8712,6 +8713,7 @@ void free_contig_range(unsigned long pfn, unsigned int nr_pages) } WARN(count != 0, "%d pages are still in use!\n", count); } +EXPORT_SYMBOL(free_contig_range); /* * The zone indicated has a new number of managed_pages; batch sizes and percpu -- 2.24.1
