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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>
This commit is contained in:
Matthew Wilcox 2023-07-27 21:39:44 +01:00 committed by Andrew Morton
parent 108c3dc6cd
commit 866ff80176
1 changed files with 7 additions and 7 deletions
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14
mm/compaction.c
View File

@ -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;