I have only now noticed that you have posted this few days ago http://lkml.kernel.org/r/1525704627-30114-1-git-send-email-yehs1@xxxxxxxxxx There were some good questions asked there and I have many that are common yet they are not covered in the cover letter. Please _always_ make sure to answer review comments before reposting. Otherwise some important parts gets lost on the way. On Thu 10-05-18 09:57:59, Michal Hocko wrote: > On Tue 08-05-18 10:30:22, Huaisheng Ye wrote: > > Traditionally, NVDIMMs are treated by mm(memory management) subsystem as > > DEVICE zone, which is a virtual zone and both its start and end of pfn > > are equal to 0, mm wouldn’t manage NVDIMM directly as DRAM, kernel uses > > corresponding drivers, which locate at \drivers\nvdimm\ and > > \drivers\acpi\nfit and fs, to realize NVDIMM memory alloc and free with > > memory hot plug implementation. > > > > With current kernel, many mm’s classical features like the buddy > > system, swap mechanism and page cache couldn’t be supported to NVDIMM. > > What we are doing is to expand kernel mm’s capacity to make it to handle > > NVDIMM like DRAM. Furthermore we make mm could treat DRAM and NVDIMM > > separately, that means mm can only put the critical pages to NVDIMM > > zone, here we created a new zone type as NVM zone. > > How do you define critical pages? Who is allowed to allocate from them? > You do not seem to add _any_ user of GFP_NVM. > > > That is to say for > > traditional(or normal) pages which would be stored at DRAM scope like > > Normal, DMA32 and DMA zones. But for the critical pages, which we hope > > them could be recovered from power fail or system crash, we make them > > to be persistent by storing them to NVM zone. > > This brings more questions than it answers. First of all is this going > to be any guarantee? Let's say I want GFP_NVM, can I get memory from > other zones? In other words is such a request allowed to fallback to > succeed? Are we allowed to reclaim memory from the new zone? What should > happen on the OOM? How is the user expected to restore the previous > content after reboot/crash? > > I am sorry if these questions are answered in the respective patches but > it would be great to have this in the cover letter to have a good > overview of the whole design. From my quick glance over patches my > previous concerns about an additional zone still hold, though. > -- > Michal Hocko > SUSE Labs -- Michal Hocko SUSE Labs
