On Tue, Dec 14, 2021 at 11:38:47AM +0100, Michal Hocko wrote: >On Tue 14-12-21 11:33:41, Christoph Lameter wrote: >> On Tue, 14 Dec 2021, Michal Hocko wrote: >> >> > This patch takes a different approach (following a lead of [3]) and it >> > pre allocates pgdat for all possible nodes in an arch indipendent code >> > - free_area_init. All uninitialized nodes are treated as memoryless >> > nodes. node_state of the node is not changed because that would lead to >> > other side effects - e.g. sysfs representation of such a node and from >> > past discussions [4] it is known that some tools might have problems >> > digesting that. >> >> Would it be possible to define a pgdat statically and place it in read >> only memory? Populate with values that ensure that the page allocator >> does not blow up but does a defined fallback. >> >> Point the pgdat for all nodes not online to that readonly pgdat? >> >> Maybe that would save some memory. When the node comes online then a real >> pgdat could be allocated. > >This is certainly possible but also it is more complex. I aim for as >simple as possible at this stage. The reason I am not concerned about >memory overhead so much (even though the pgdat is a large data >structure) is that these unpopulated nodes are rather rare. We might see >more of them in the future but we are not quite there yet so I do not >think this is a major obstacle for now. Another thing is we still have a chance to get NULL NODE_DATA if we failed to allocate it. And this is the problem we want to address here. This is not urgent, while we may need to address this later. > >-- >Michal Hocko >SUSE Labs -- Wei Yang Help you, Help me
