[RFC PATCH v11 10/29] mm: Add AS_UNMOVABLE to mark mapping as completely unmovable

[Sean Christopherson]

Signed-off-by: Sean Christopherson <sea...@google.com>
---
 include/linux/pagemap.h | 11 +++++++++++
 mm/compaction.c         |  4 ++++
 mm/migrate.c            |  2 ++
 3 files changed, 17 insertions(+)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 716953ee1ebd..931d2f1da7d5 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -203,6 +203,7 @@ enum mapping_flags {
        /* writeback related tags are not used */
        AS_NO_WRITEBACK_TAGS = 5,
        AS_LARGE_FOLIO_SUPPORT = 6,
+       AS_UNMOVABLE    = 7,    /* The mapping cannot be moved, ever */
 };
 
 /**
@@ -273,6 +274,16 @@ static inline int mapping_use_writeback_tags(struct 
address_space *mapping)
        return !test_bit(AS_NO_WRITEBACK_TAGS, &mapping->flags);
 }
 
+static inline void mapping_set_unmovable(struct address_space *mapping)
+{
+       set_bit(AS_UNMOVABLE, &mapping->flags);
+}
+
+static inline bool mapping_unmovable(struct address_space *mapping)
+{
+       return test_bit(AS_UNMOVABLE, &mapping->flags);
+}
+
 static inline gfp_t mapping_gfp_mask(struct address_space * mapping)
 {
        return mapping->gfp_mask;
diff --git a/mm/compaction.c b/mm/compaction.c
index dbc9f86b1934..a3d2b132df52 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1047,6 +1047,10 @@ isolate_migratepages_block(struct compact_control *cc, 
unsigned long low_pfn,
                if (!mapping && (folio_ref_count(folio) - 1) > 
folio_mapcount(folio))
                        goto isolate_fail_put;
 
+               /* The mapping truly isn't movable. */
+               if (mapping && mapping_unmovable(mapping))
+                       goto isolate_fail_put;
+
                /*
                 * Only allow to migrate anonymous pages in GFP_NOFS context
                 * because those do not depend on fs locks.
diff --git a/mm/migrate.c b/mm/migrate.c
index 24baad2571e3..c00a4ca86698 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -954,6 +954,8 @@ static int move_to_new_folio(struct folio *dst, struct 
folio *src,
 
                if (!mapping)
                        rc = migrate_folio(mapping, dst, src, mode);
+               else if (mapping_unmovable(mapping))
+                       rc = -EOPNOTSUPP;
                else if (mapping->a_ops->migrate_folio)
                        /*
                         * Most folios have a mapping and most filesystems
-- 
2.41.0.255.g8b1d071c50-goog