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Memory blocks can be onlined in random order. When this order is not natural some memory pages are not onlined because of the redundant check in hv_online_page(). Here is a real world scenario: 1) Host tries to hot-add the following (process_hot_add): pg_start=rg_start=0x48000, pfn_cnt=111616, rg_size=262144 2) This results in adding 4 memory blocks: [ 109.057866] init_memory_mapping: [mem 0x48000000-0x4fffffff] [ 114.102698] init_memory_mapping: [mem 0x50000000-0x57ffffff] [ 119.168039] init_memory_mapping: [mem 0x58000000-0x5fffffff] [ 124.233053] init_memory_mapping: [mem 0x60000000-0x67ffffff] The last one is incomplete but we have special has->covered_end_pfn counter to avoid onlining non-backed frames and hv_bring_pgs_online() function to bring them online later on. 3) Now we have 4 offline memory blocks: /sys/devices/system/memory/memory9-12 $ for f in /sys/devices/system/memory/memory*/state; do echo $f `cat $f`; done | grep -v onlin /sys/devices/system/memory/memory10/state offline /sys/devices/system/memory/memory11/state offline /sys/devices/system/memory/memory12/state offline /sys/devices/system/memory/memory9/state offline 4) We bring them online in non-natural order: $grep MemTotal /proc/meminfo MemTotal: 966348 kB $echo online > /sys/devices/system/memory/memory12/state && grep MemTotal /proc/meminfo MemTotal: 1019596 kB $echo online > /sys/devices/system/memory/memory11/state && grep MemTotal /proc/meminfo MemTotal: 1150668 kB $echo online > /sys/devices/system/memory/memory9/state && grep MemTotal /proc/meminfo MemTotal: 1150668 kB As you can see memory9 block gives us zero additional memory. We can also observe a huge discrepancy between host- and guest-reported memory sizes. The root cause of the issue is the redundant pg >= covered_start_pfn check (and covered_start_pfn advancing) in hv_online_page(). When upper memory block in being onlined before the lower one (memory12 and memory11 in the above case) we advance the covered_start_pfn pointer and all memory9 pages do not pass the check. If the assumption that host always gives us requests in sequential order and pg_start always equals rg_start when the first request for the new HA region is received (that's the case in my testing) is correct than we can get rid of covered_start_pfn and pg >= start_pfn check in hv_online_page() is sufficient. The current char-next branch is broken and this patch fixes the bug. Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com> Signed-off-by: K. Y. Srinivasan <kys@microsoft.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
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| .. | ||
| channel_mgmt.c | ||
| channel.c | ||
| connection.c | ||
| hv_balloon.c | ||
| hv_fcopy.c | ||
| hv_kvp.c | ||
| hv_snapshot.c | ||
| hv_util.c | ||
| hv.c | ||
| hyperv_vmbus.h | ||
| Kconfig | ||
| Makefile | ||
| ring_buffer.c | ||
| vmbus_drv.c | ||