Messages in this thread | | | Date | Wed, 26 Jun 2019 10:27:56 +0200 | From | Oscar Salvador <> | Subject | Re: [PATCH v2 0/5] Allocate memmap from hotadded memory |
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On Wed, Jun 26, 2019 at 10:15:16AM +0200, Oscar Salvador wrote: > On Wed, Jun 26, 2019 at 10:11:06AM +0200, David Hildenbrand wrote: > > Back then, I already mentioned that we might have some users that > > remove_memory() they never added in a granularity it wasn't added. My > > concerns back then were never fully sorted out. > > > > arch/powerpc/platforms/powernv/memtrace.c > > > > - Will remove memory in memory block size chunks it never added > > - What if that memory resides on a DIMM added via MHP_MEMMAP_DEVICE? > > > > Will it at least bail out? Or simply break? > > > > IOW: I am not yet 100% convinced that MHP_MEMMAP_DEVICE is save to be > > introduced. > > Uhm, I will take a closer look and see if I can clear your concerns. > TBH, I did not try to use arch/powerpc/platforms/powernv/memtrace.c > yet. > > I will get back to you once I tried it out.
On a second though, it would be quite trivial to implement a check in remove_memory() that does not allow to remove memory used with MHP_MEMMAP_DEVICE in a different granularity:
+static bool check_vmemmap_granularity(u64 start, u64 size); +{ + unsigned long pfn; + unsigned int nr_pages; + struct page *p; + + pfn = PHYS_PFN(start); + p = pfn_to_page(pfn); + nr_pages = size >> PAGE_SIZE; + + if (PageVmemmap(p)) { + struct page *h = vmemmap_get_head(p); + unsigned long sections = (unsigned long)h->private; + + if (sections * PAGES_PER_SECTION > nr_pages) + fail; + } + no_fail; +} + + static int __ref try_remove_memory(int nid, u64 start, u64 size) { int rc = 0; BUG_ON(check_hotplug_memory_range(start, size)); mem_hotplug_begin(); + rc = check_vmemmap_granularity(start, size); + if (rc) + goto done;
The above is quite hacky, but it gives an idea. I will try the code from arch/powerpc/platforms/powernv/memtrace.c and see how can I implement a check.
-- Oscar Salvador SUSE L3
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