migrate_pages: move THP/hugetlb migration support check to simplify code

This is a code cleanup patch, no functionality change is expected.  After
the change, the line number reduces especially in the long
migrate_pages_batch().

Link: https://lkml.kernel.org/r/20230213123444.155149-10-ying.huang@intel.com
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Suggested-by: Alistair Popple <apopple@nvidia.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Bharata B Rao <bharata@amd.com>
Cc: Xin Hao <xhao@linux.alibaba.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/migrate.c b/mm/migrate.c
index 2fa420e..ef68a1a 100644 (file)
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1117,9 +1117,6 @@ static int migrate_folio_unmap(new_page_t get_new_page, free_page_t put_new_page
        bool locked = false;
        bool dst_locked = false;
 
-       if (!thp_migration_supported() && folio_test_transhuge(src))
-               return -ENOSYS;
-
        if (folio_ref_count(src) == 1) {
                /* Folio was freed from under us. So we are done. */
                folio_clear_active(src);
@@ -1380,16 +1377,6 @@ static int unmap_and_move_huge_page(new_page_t get_new_page,
        struct anon_vma *anon_vma = NULL;
        struct address_space *mapping = NULL;
 
-       /*
-        * Migratability of hugepages depends on architectures and their size.
-        * This check is necessary because some callers of hugepage migration
-        * like soft offline and memory hotremove don't walk through page
-        * tables or check whether the hugepage is pmd-based or not before
-        * kicking migration.
-        */
-       if (!hugepage_migration_supported(page_hstate(hpage)))
-               return -ENOSYS;
-
        if (folio_ref_count(src) == 1) {
                /* page was freed from under us. So we are done. */
                folio_putback_active_hugetlb(src);
@@ -1556,6 +1543,20 @@ static int migrate_hugetlbs(struct list_head *from, new_page_t get_new_page,
 
                        cond_resched();
 
+                       /*
+                        * Migratability of hugepages depends on architectures and
+                        * their size.  This check is necessary because some callers
+                        * of hugepage migration like soft offline and memory
+                        * hotremove don't walk through page tables or check whether
+                        * the hugepage is pmd-based or not before kicking migration.
+                        */
+                       if (!hugepage_migration_supported(folio_hstate(folio))) {
+                               nr_failed++;
+                               stats->nr_failed_pages += nr_pages;
+                               list_move_tail(&folio->lru, ret_folios);
+                               continue;
+                       }
+
                        rc = unmap_and_move_huge_page(get_new_page,
                                                      put_new_page, private,
                                                      &folio->page, pass > 2, mode,
@@ -1565,16 +1566,9 @@ static int migrate_hugetlbs(struct list_head *from, new_page_t get_new_page,
                         *      Success: hugetlb folio will be put back
                         *      -EAGAIN: stay on the from list
                         *      -ENOMEM: stay on the from list
-                        *      -ENOSYS: stay on the from list
                         *      Other errno: put on ret_folios list
                         */
                        switch(rc) {
-                       case -ENOSYS:
-                               /* Hugetlb migration is unsupported */
-                               nr_failed++;
-                               stats->nr_failed_pages += nr_pages;
-                               list_move_tail(&folio->lru, ret_folios);
-                               break;
                        case -ENOMEM:
                                /*
                                 * When memory is low, don't bother to try to migrate
@@ -1664,6 +1658,28 @@ retry:
 
                        cond_resched();
 
+                       /*
+                        * Large folio migration might be unsupported or
+                        * the allocation might be failed so we should retry
+                        * on the same folio with the large folio split
+                        * to normal folios.
+                        *
+                        * Split folios are put in split_folios, and
+                        * we will migrate them after the rest of the
+                        * list is processed.
+                        */
+                       if (!thp_migration_supported() && is_thp) {
+                               nr_large_failed++;
+                               stats->nr_thp_failed++;
+                               if (!try_split_folio(folio, &split_folios)) {
+                                       stats->nr_thp_split++;
+                                       continue;
+                               }
+                               stats->nr_failed_pages += nr_pages;
+                               list_move_tail(&folio->lru, ret_folios);
+                               continue;
+                       }
+
                        rc = migrate_folio_unmap(get_new_page, put_new_page, private,
                                                 folio, &dst, pass > 2, avoid_force_lock,
                                                 mode, reason, ret_folios);
@@ -1675,36 +1691,9 @@ retry:
                         *      -EAGAIN: stay on the from list
                         *      -EDEADLOCK: stay on the from list
                         *      -ENOMEM: stay on the from list
-                        *      -ENOSYS: stay on the from list
                         *      Other errno: put on ret_folios list
                         */
                        switch(rc) {
-                       /*
-                        * Large folio migration might be unsupported or
-                        * the allocation could've failed so we should retry
-                        * on the same folio with the large folio split
-                        * to normal folios.
-                        *
-                        * Split folios are put in split_folios, and
-                        * we will migrate them after the rest of the
-                        * list is processed.
-                        */
-                       case -ENOSYS:
-                               /* Large folio migration is unsupported */
-                               if (is_large) {
-                                       nr_large_failed++;
-                                       stats->nr_thp_failed += is_thp;
-                                       if (!try_split_folio(folio, &split_folios)) {
-                                               stats->nr_thp_split += is_thp;
-                                               break;
-                                       }
-                               } else if (!no_split_folio_counting) {
-                                       nr_failed++;
-                               }
-
-                               stats->nr_failed_pages += nr_pages;
-                               list_move_tail(&folio->lru, ret_folios);
-                               break;
                        case -ENOMEM:
                                /*
                                 * When memory is low, don't bother to try to migrate