mm: improve the comment in isolate_migratepages_block()

A recent patch shows that not everybody understands that "stabilise the
mapping" really means "prevent the mapping from being freed", so change
the wording to hopefully make that more clear.

Link: https://lkml.kernel.org/r/ZMLWEB4m3zvX6SBN@casper.infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/compaction.c b/mm/compaction.c
index e6ac0ef4c178f141e14e32535d2c3ee5f8e7f89c..c4d3a3129fd53514976549dc8e3bba1b6c1113dd 100644 (file)
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1100,13 +1100,13 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
                        bool migrate_dirty;
 
                        /*
-                        * Only pages without mappings or that have a
-                        * ->migrate_folio callback are possible to migrate
-                        * without blocking. However, we can be racing with
-                        * truncation so it's necessary to lock the page
-                        * to stabilise the mapping as truncation holds
-                        * the page lock until after the page is removed
-                        * from the page cache.
+                        * Only folios without mappings or that have
+                        * a ->migrate_folio callback are possible to
+                        * migrate without blocking.  However, we may
+                        * be racing with truncation, which can free
+                        * the mapping.  Truncation holds the folio lock
+                        * until after the folio is removed from the page
+                        * cache so holding it ourselves is sufficient.
                         */
                        if (!folio_trylock(folio))
                                goto isolate_fail_put;