Commit 866ff801 authored by Matthew Wilcox's avatar Matthew Wilcox Committed by Andrew Morton
Browse files

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: default avatarMatthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: default avatarDavid Hildenbrand <david@redhat.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 108c3dc6

mm/compaction.c

+7 −7
Original line number Diff line number Diff line
@@ -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;