[RFC PATCH v3 2/7] mm: make alloc_demote_folio externally invokable for migration

[Honggyu Kim]

The alloc_demote_folio can be used out of vmscan.c so it'd be better to
remove static keyword from it.

This function can also be used for both demotion and promotion so it'd
be better to rename it from alloc_demote_folio to alloc_migrate_folio.

Signed-off-by: Honggyu Kim <honggyu....@sk.com>
---
 mm/internal.h |  1 +
 mm/vmscan.c   | 10 +++++++---
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/mm/internal.h b/mm/internal.h
index f309a010d50f..c96ff9bc82d0 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -866,6 +866,7 @@ extern unsigned long  __must_check vm_mmap_pgoff(struct 
file *, unsigned long,
         unsigned long, unsigned long);
 
 extern void set_pageblock_order(void);
+struct folio *alloc_migrate_folio(struct folio *src, unsigned long private);
 unsigned long reclaim_pages(struct list_head *folio_list);
 unsigned int reclaim_clean_pages_from_list(struct zone *zone,
                                            struct list_head *folio_list);
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 4255619a1a31..9e456cac03b4 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -910,8 +910,7 @@ static void folio_check_dirty_writeback(struct folio *folio,
                mapping->a_ops->is_dirty_writeback(folio, dirty, writeback);
 }
 
-static struct folio *alloc_demote_folio(struct folio *src,
-               unsigned long private)
+struct folio *alloc_migrate_folio(struct folio *src, unsigned long private)
 {
        struct folio *dst;
        nodemask_t *allowed_mask;
@@ -935,6 +934,11 @@ static struct folio *alloc_demote_folio(struct folio *src,
        if (dst)
                return dst;
 
+       /*
+        * Allocation failed from the target node so try to allocate from
+        * fallback nodes based on allowed_mask.
+        * See fallback_alloc() at mm/slab.c.
+        */
        mtc->gfp_mask &= ~__GFP_THISNODE;
        mtc->nmask = allowed_mask;
 
@@ -973,7 +977,7 @@ static unsigned int demote_folio_list(struct list_head 
*demote_folios,
        node_get_allowed_targets(pgdat, &allowed_mask);
 
        /* Demotion ignores all cpuset and mempolicy settings */
-       migrate_pages(demote_folios, alloc_demote_folio, NULL,
+       migrate_pages(demote_folios, alloc_migrate_folio, NULL,
                      (unsigned long)&mtc, MIGRATE_ASYNC, MR_DEMOTION,
                      &nr_succeeded);
 
-- 
2.34.1