Re: [PATCH 1/2] mm: drop migrate type checks from has_unmovable_pages

[Michael Ellerman]

Michal Hocko <mhocko@xxxxxxxxxx> writes:

> From: Michal Hocko <mhocko@xxxxxxxx>
>
> 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@xxxxxxxxxxxxxx>
> Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>

Thanks, that works for me.

Tested-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>

cheers