| Message ID | ZMLWEB4m3zvX6SBN@casper.infradead.org (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm: Improve the comment in isolate_migratepages_block() | expand |
On 27.07.23 22:39, Matthew Wilcox wrote: > 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. > > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> > > diff --git a/mm/compaction.c b/mm/compaction.c > index 9641e2131901..9be2c3504ff2 100644 > --- a/mm/compaction.c > +++ b/mm/compaction.c > @@ -1095,13 +1095,13 @@ 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; > Reviewed-by: David Hildenbrand <david@redhat.com>
diff --git a/mm/compaction.c b/mm/compaction.c index 9641e2131901..9be2c3504ff2 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -1095,13 +1095,13 @@ 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;
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. Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>