On Mon 21-10-19 16:19:25, David Hildenbrand wrote:
> 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 <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> Cc: Vlastimil Babka <vbabka@xxxxxxx>
> Cc: Oscar Salvador <osalvador@xxxxxxx>
> Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
> Cc: Mike Rapoport <rppt@xxxxxxxxxxxxx>
> Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> Cc: Wei Yang <richard.weiyang@xxxxxxxxx>
> Cc: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>
> Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx>
> Cc: Pavel Tatashin <pavel.tatashin@xxxxxxxxxxxxx>
> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
We still set PageReserved before onlining pages and that one should be
good to go as well (memmap_init_zone).
Thanks!
There is a comment above offline_isolated_pages_cb that should be
removed as well.
> ---
> mm/page_alloc.c | 5 +----
> 1 file changed, 1 insertion(+), 4 deletions(-)
>
> 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
>
--
Michal Hocko
SUSE Labs
