On 09/16/2019 02:20 PM, Anshuman Khandual wrote: > > > On 09/16/2019 12:06 PM, Mike Rapoport wrote: >> On Mon, Sep 16, 2019 at 11:17:37AM +0530, Anshuman Khandual wrote: >>> In add_memory_resource() the memory range to be hot added first gets into >>> the memblock via memblock_add() before arch_add_memory() is called on it. >>> Reverse sequence should be followed during memory hot removal which already >>> is being followed in add_memory_resource() error path. This now ensures >>> required re-order between memblock_[free|remove]() and arch_remove_memory() >>> during memory hot-remove. >>> >>> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> >>> Cc: Oscar Salvador <osalvador@xxxxxxx> >>> Cc: Michal Hocko <mhocko@xxxxxxxx> >>> Cc: David Hildenbrand <david@xxxxxxxxxx> >>> Cc: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx> >>> Cc: Dan Williams <dan.j.williams@xxxxxxxxx> >>> Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx> >>> --- >>> Original patch https://lkml.org/lkml/2019/9/3/327 >>> >>> Memory hot remove now works on arm64 without this because a recent commit >>> 60bb462fc7ad ("drivers/base/node.c: simplify unregister_memory_block_under_nodes()"). >>> >>> David mentioned that re-ordering should still make sense for consistency >>> purpose (removing stuff in the reverse order they were added). This patch >>> is now detached from arm64 hot-remove series. >>> >>> https://lkml.org/lkml/2019/9/3/326 >>> >>> mm/memory_hotplug.c | 4 ++-- >>> 1 file changed, 2 insertions(+), 2 deletions(-) >>> >>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c >>> index c73f09913165..355c466e0621 100644 >>> --- a/mm/memory_hotplug.c >>> +++ b/mm/memory_hotplug.c >>> @@ -1770,13 +1770,13 @@ static int __ref try_remove_memory(int nid, u64 start, u64 size) >>> >>> /* remove memmap entry */ >>> firmware_map_remove(start, start + size, "System RAM"); >>> - memblock_free(start, size); >>> - memblock_remove(start, size); >>> >>> /* remove memory block devices before removing memory */ >>> remove_memory_block_devices(start, size); >>> >>> arch_remove_memory(nid, start, size, NULL); >>> + memblock_free(start, size); >> >> I don't see memblock_reserve() anywhere in memory_hotplug.c, so the >> memblock_free() call here seems superfluous. I think it can be simply >> dropped. > > I had observed that previously but was not sure whether or not there are > still scenarios where it might be true. Error path in add_memory_resource() > even just calls memblock_remove() not memblock_free(). Unless there is any > objection, can just drop it. Hello Mike, Looks like we might need memblock_free() here as well. As you mentioned before there might not be any memblock_reserve() in mm/memory_hotplug.c but that does not guarantee that there could not have been a previous memblock_reserve() or memblock_alloc_XXX() allocation which came from the current hot remove range. memblock_free() followed by memblock_remove() on the entire hot-remove range ensures that memblock.memory and memblock.reserve are in sync and the entire range is guaranteed to be removed from both the memory types. Or am I missing something here. - Anshuman
