On Tue, Feb 02, 2021 at 09:35:09AM +0100, David Hildenbrand wrote: > Yeah, last time I raised it was in > > https://lkml.kernel.org/r/20200703013435.GA11340@L-31X9LVDL-1304.local > > but I never got to clean it up myself. I see. > > So, IIRC we have two cases during hotplug: > > 1) the ones that want memory blocks > > 2) the ones that do not want them (pmem stuff) > > > > For #1, we always enforce section alignment in add_memory_resource, and for > > #2 we always make sure the range is at least sub-section aligned. > > > > And the important stuff is that boot memory is no longer to be hot-removed > > (boot memory had some strange layout sometimes). > > The vmemmap of boot mem sections is always fully populated, even with > strange memory layouts (e.g., see comment in pfn_valid()). In addition, we > can only offline+remove whole sections, so that should be fine. You are right. > > > > > So, given the above, I think it should be safe to drop that check in > > remote_pte_table. > > But do we really need to force page alignment in vmemmap_populate/vmemmap_free? > > vmemmap_populate should already receive a page-aligned chunk because > > __populate_section_memmap made sure of that, and vmemmap_free() should be ok > > as we already filtered out at hot-adding stage. > > > > Of course, this will hold as long as struct page size of multiple of 8. > > Should that change we might get trouble, but I do not think that can ever > > happened (tm). > > > > But anyway, I am fine with placing a couple of checks in vmemmap_{populate,free} > > just to double check. > > > > What do you think? > > I'd just throw in 1 or 2 VM_BUG_ON() to self-document what we expect and > that we thought about these conditions. It's then easy to identify the > relevant commit where we explain the rationale. Fine by me, also on a second thought it is good to have some sort of clue when looking at the code. I will add that cleanup before the actual "fix" of the sub-pmd stuff. thanks! -- Oscar Salvador SUSE L3
