mm: memory-hotplug: enable memory hotplug to handle hugepage

Until now we can't offline memory blocks which contain hugepages because a
hugepage is considered as an unmovable page.  But now with this patch
series, a hugepage has become movable, so by using hugepage migration we
can offline such memory blocks.

What's different from other users of hugepage migration is that we need to
decompose all the hugepages inside the target memory block into free buddy
pages after hugepage migration, because otherwise free hugepages remaining
in the memory block intervene the memory offlining.  For this reason we
introduce new functions dissolve_free_huge_page() and
dissolve_free_huge_pages().

Other than that, what this patch does is straightforwardly to add hugepage
migration code, that is, adding hugepage code to the functions which scan
over pfn and collect hugepages to be migrated, and adding a hugepage
allocation function to alloc_migrate_target().

As for larger hugepages (1GB for x86_64), it's not easy to do hotremove
over them because it's larger than memory block.  So we now simply leave
it to fail as it is.

[yongjun_wei@trendmicro.com.cn: remove duplicated include]
Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Acked-by: Andi Kleen <ak@linux.intel.com>
Cc: Hillf Danton <dhillf@gmail.com>
Cc: Wanpeng Li <liwanp@linux.vnet.ibm.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Hugh Dickins <hughd@google.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Rik van Riel <riel@redhat.com>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 11 insertions, 0 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 7c3f8d7e2d8e..f7cc08dad26a 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6008,6 +6008,17 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
                         continue;
 
                 page = pfn_to_page(check);
+
+                /*
+                 * Hugepages are not in LRU lists, but they're movable.
+                 * We need not scan over tail pages bacause we don't
+                 * handle each tail page individually in migration.
+                 */
+                if (PageHuge(page)) {
+                        iter = round_up(iter + 1, 1<<compound_order(page)) - 1;
+                        continue;
+                }
+
                 /*
                  * We can't use page_count without pin a page
                  * because another CPU can free compound page.