mm/memory hotplug/unplug: Fix zone going non-contiguous after new memory is plugged #1
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mm/memory hotplug: Fix zone->contiguous always false when hotplug Function set_zone_contiguous used __pageblock_pfn_to_page to check the whole pageblock is in the same zone. One assumption is the memory section must online, otherwise the __pageblock_pfn_to_page will return NULL, then the set_zone_contiguous will be false. When move_pfn_range_to_zone invoked set_zone_contiguous, since the memory section did not online, the return value will always be false. To fix this issue, we removed the set_zone_contiguous from the move_pfn_range_to_zone, and place it after memory section onlined. Function remove_pfn_range_from_zone did not have this issue because memory section remains online at the time set_zone_contiguous invoked. |
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This series contains 2 patches, the first one add a fast path to check the zone->contiguous, the second one fix an issue when check the zone->contiguous at the slow path during zone grows. |
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This series contains 2 patches, the first one add a fast path to check the zone->contiguous, the second one fix an issue when check the zone->contiguous at the slow path during zone grows. The issue fixed by the second patch can be found in the original code path without the first patch. |
Function set_zone_contiguous used __pageblock_pfn_to_page to check the whole pageblock is in the same zone. One assumption is the memory section must online, otherwise the __pageblock_pfn_to_page will return NULL, then the set_zone_contiguous will be false. When move_pfn_range_to_zone invoked set_zone_contiguous, since the memory section did not online, the return value will always be false. To fix this issue, we removed the set_zone_contiguous from the move_pfn_range_to_zone, and place it after memory section onlined. Function remove_pfn_range_from_zone did not have this issue because memory section remains online at the time set_zone_contiguous invoked. Reviewed-by: Tianyou Li <tianyou.li@intel.com> Reviewed-by: Nanhai Zou <nanhai.zou@intel.com> Signed-off-by: Liu, Yuan1 <yuan1.liu@intel.com>
when new memory is plugged, set_zone_contiguous will never set the zone as contiguous, because the memory section of the newly plugged memory is still offline during the zone contiguity check.
if the memory section of the pfn is offline, __pageblock_pfn_to_page cannot return a page for that pfn, causing set_zone_contiguous to skip setting zone->contiguous.
The fix is to move set_zone_contiguous after online_mem_sections, ensuring that the newly plugged memory is already onlined before the set_zone_contiguous.
Reviewed-by: Tianyou Li tianyou.li@intel.com
Reviewed-by: Nanhai Zou nanhai.zou@intel.com
Signed-off-by: Liu, Yuan1 yuan1.liu@intel.com