On Mon 02-03-20 14:49:34, David Hildenbrand wrote: > 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). Same feedback as in pxm_to_node export. No objections to exporting the symbol but it would be better to squash this function into the patch which uses it. The changelog is highly virtio-mem specific anyway. Maybe it is just a dejavu but I feel I have already said that but I do not remember any details. > 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 -- Michal Hocko SUSE Labs
