On Thu 19-09-19 16:22:23, 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). Is there any real reason to export as GPL rather than generic EXPORT_SYMBOL? In other words do we need to restrict the usage this interface only to GPL modules and why if so. All other allocator APIs are EXPORT_SYMBOL so there should better be a good reason for this one to differ. I can understand that this one is slightly different by requesting a specific range of the memory but it is still under a full control of the core MM to say no. > 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> > Signed-off-by: David Hildenbrand <david@xxxxxxxxxx> Other than that, I do not think exporting this function is harmful. It would be worse to reinvent it and do it wrong. I usually prefer to add a caller in the same patch, though, because it makes the usage explicit and clear. Acked-by: Michal Hocko <mhocko@xxxxxxxx> # to export contig range allocator API > --- > mm/page_alloc.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 3334a769eb91..d5d7944954b3 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -8469,6 +8469,7 @@ int alloc_contig_range(unsigned long start, unsigned long end, > pfn_max_align_up(end), migratetype); > return ret; > } > +EXPORT_SYMBOL_GPL(alloc_contig_range); > #endif /* CONFIG_CONTIG_ALLOC */ > > void free_contig_range(unsigned long pfn, unsigned int nr_pages) > @@ -8483,6 +8484,7 @@ void free_contig_range(unsigned long pfn, unsigned int nr_pages) > } > WARN(count != 0, "%d pages are still in use!\n", count); > } > +EXPORT_SYMBOL_GPL(free_contig_range); > > #ifdef CONFIG_MEMORY_HOTPLUG > /* > -- > 2.21.0 -- Michal Hocko SUSE Labs
