mm: drop migrate type checks from has_unmovable_pages

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.

[akpm@linux-foundation.org: remove unused local `mt']
Link: http://lkml.kernel.org/r/20171013120013.698-1-mhocko@kernel.org
Signed-off-by: Michal Hocko <mhocko@suse.com>
Reported-by: Michael Ellerman <mpe@ellerman.id.au>
Tested-by: Michael Ellerman <mpe@ellerman.id.au>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Tested-by: Tony Lindgren <tony@atomide.com>
Tested-by: Ran Wang <ran.wang_1@nxp.com>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Reza Arbab <arbab@linux.vnet.ibm.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Xishi Qiu <qiuxishi@huawei.com>
Cc: Yasuaki Ishimatsu <yasu.isimatu@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 77e4d3c5c57b72dcd7e411a03707c26dc85c7c04..e6d4234e0d1a0d481e0b055617b2df34dbf1ab05 100644 (file)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -7356,7 +7356,6 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
                         bool skip_hwpoisoned_pages)
 {
        unsigned long pfn, iter, found;
-       int mt;
 
        /*
         * For avoiding noise data, lru_add_drain_all() should be called
@@ -7364,9 +7363,6 @@ 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++) {