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SubjectRe: [PATCH 1/2] mm: drop migrate type checks from has_unmovable_pages
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On 10/13/2017 02:00 PM, Michal Hocko wrote:
> From: Michal Hocko <mhocko@suse.com>
>
> Michael has noticed that the memory offline tries to migrate kernel code
> pages when doing
> echo 0 > /sys/devices/system/memory/memory0/online
>
> The current implementation will fail the operation after several failed
> page migration attempts but we shouldn't even attempt to migrate
> that memory and fail right away because this memory is clearly not
> migrateable. This will become a real problem when we drop the retry loop
> counter resp. timeout.
>
> The real problem is in has_unmovable_pages in fact. We should fail if
> there are any non migrateable pages in the area. In orther to guarantee
> that remove the migrate type checks because MIGRATE_MOVABLE is not
> guaranteed to contain only migrateable pages. It is merely a heuristic.
> Similarly MIGRATE_CMA does guarantee that the page allocator doesn't
> allocate any non-migrateable pages from the block but CMA allocations
> themselves are unlikely to migrateable. Therefore remove both checks.
>
> Reported-by: Michael Ellerman <mpe@ellerman.id.au>
> Signed-off-by: Michal Hocko <mhocko@suse.com>

Acked-by: Vlastimil Babka <vbabka@suse.cz>

> ---
> mm/page_alloc.c | 3 ---
> 1 file changed, 3 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 3badcedf96a7..ad0294ab3e4f 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -7355,9 +7355,6 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
> */
> if (zone_idx(zone) == ZONE_MOVABLE)
> return false;
> - mt = get_pageblock_migratetype(page);
> - if (mt == MIGRATE_MOVABLE || is_migrate_cma(mt))
> - return false;
>
> pfn = page_to_pfn(page);
> for (found = 0, iter = 0; iter < pageblock_nr_pages; iter++) {
>

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