We call __offline_isolated_pages() from __offline_pages() after all pages were isolated and are either free (PageBuddy()) or PageHWPoison. Nothing can stop us from offlining memory at this point.
In __offline_isolated_pages() we first set all affected memory sections offline (offline_mem_sections(pfn, end_pfn)), to mark the memmap as invalid (pfn_to_online_page() will no longer succeed), and then walk over all pages to pull the free pages from the free lists (to the isolated free lists, to be precise). Note that re-onlining a memory block will result in the whole memmap getting reinitialized, overwriting any old state. We already poision the memmap when offlining is complete to find any access to stale/uninitialized memmaps. So, setting the pages PageReserved() is not helpful. The memap is marked offline and all pageblocks are isolated. As soon as offline, the memmap is stale either way. This looks like a leftover from ancient times where we initialized the memmap when adding memory and not when onlining it (the pages were set PageReserved so re-onling would work as expected). Cc: Andrew Morton <[email protected]> Cc: Michal Hocko <[email protected]> Cc: Vlastimil Babka <[email protected]> Cc: Oscar Salvador <[email protected]> Cc: Mel Gorman <[email protected]> Cc: Mike Rapoport <[email protected]> Cc: Dan Williams <[email protected]> Cc: Wei Yang <[email protected]> Cc: Alexander Duyck <[email protected]> Cc: Anshuman Khandual <[email protected]> Cc: Pavel Tatashin <[email protected]> Acked-by: Michal Hocko <[email protected]> Signed-off-by: David Hildenbrand <[email protected]> --- mm/memory_hotplug.c | 4 +--- mm/page_alloc.c | 5 +---- 2 files changed, 2 insertions(+), 7 deletions(-) diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c index 5e6b2a312362..3524e2e1a9df 100644 --- a/mm/memory_hotplug.c +++ b/mm/memory_hotplug.c @@ -1346,9 +1346,7 @@ do_migrate_range(unsigned long start_pfn, unsigned long end_pfn) return ret; } -/* - * remove from free_area[] and mark all as Reserved. - */ +/* Mark all sections offline and remove all free pages from the buddy. */ static int offline_isolated_pages_cb(unsigned long start, unsigned long nr_pages, void *data) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index ed8884dc0c47..bf6b21f02154 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -8667,7 +8667,7 @@ __offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn) { struct page *page; struct zone *zone; - unsigned int order, i; + unsigned int order; unsigned long pfn; unsigned long flags; unsigned long offlined_pages = 0; @@ -8695,7 +8695,6 @@ __offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn) */ if (unlikely(!PageBuddy(page) && PageHWPoison(page))) { pfn++; - SetPageReserved(page); offlined_pages++; continue; } @@ -8709,8 +8708,6 @@ __offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn) pfn, 1 << order, end_pfn); #endif del_page_from_free_area(page, &zone->free_area[order]); - for (i = 0; i < (1 << order); i++) - SetPageReserved((page+i)); pfn += (1 << order); } spin_unlock_irqrestore(&zone->lock, flags); -- 2.21.0
