mm, migration: add destination page freeing callback

Memory migration uses a callback defined by the caller to determine how to
allocate destination pages.  When migration fails for a source page,
however, it frees the destination page back to the system.

This patch adds a memory migration callback defined by the caller to
determine how to free destination pages.  If a caller, such as memory
compaction, builds its own freelist for migration targets, this can reuse
already freed memory instead of scanning additional memory.

If the caller provides a function to handle freeing of destination pages,
it is called when page migration fails.  If the caller passes NULL then
freeing back to the system will be handled as usual.  This patch
introduces no functional change.

Signed-off-by: David Rientjes <rientjes@google.com>
Reviewed-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Greg Thelen <gthelen@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 2 deletions

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 7f7864b95e8e..16bc9fa42998 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1028,7 +1028,7 @@ static int migrate_to_node(struct mm_struct *mm, int source, int dest,
                         flags | MPOL_MF_DISCONTIG_OK, &pagelist);
 
         if (!list_empty(&pagelist)) {
-                err = migrate_pages(&pagelist, new_node_page, dest,
+                err = migrate_pages(&pagelist, new_node_page, NULL, dest,
                                         MIGRATE_SYNC, MR_SYSCALL);
                 if (err)
                         putback_movable_pages(&pagelist);
@@ -1277,7 +1277,7 @@ static long do_mbind(unsigned long start, unsigned long len,
                 if (!list_empty(&pagelist)) {
                         WARN_ON_ONCE(flags & MPOL_MF_LAZY);
                         nr_failed = migrate_pages(&pagelist, new_vma_page,
-                                        (unsigned long)vma,
+                                        NULL, (unsigned long)vma,
                                         MIGRATE_SYNC, MR_MEMPOLICY_MBIND);
                         if (nr_failed)
                                 putback_movable_pages(&pagelist);