mm: remove stale example from comment
folio_add_new_anon_rmap() no longer works this way, so just remove the entire example. Link: https://lkml.kernel.org/r/20231211162214.2146080-6-willy@infradead.org Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> Reviewed-by: David Hildenbrand <david@redhat.com> Cc: Ralph Campbell <rcampbell@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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@ -473,21 +473,11 @@ void free_zone_device_page(struct page *page)
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__ClearPageAnonExclusive(page);
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__ClearPageAnonExclusive(page);
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/*
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/*
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* When a device managed page is freed, the page->mapping field
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* When a device managed page is freed, the folio->mapping field
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* may still contain a (stale) mapping value. For example, the
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* may still contain a (stale) mapping value. For example, the
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* lower bits of page->mapping may still identify the page as an
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* lower bits of folio->mapping may still identify the folio as an
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* anonymous page. Ultimately, this entire field is just stale
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* anonymous folio. Ultimately, this entire field is just stale
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* and wrong, and it will cause errors if not cleared. One
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* and wrong, and it will cause errors if not cleared.
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* example is:
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*
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* migrate_vma_pages()
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* migrate_vma_insert_page()
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* page_add_new_anon_rmap()
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* __page_set_anon_rmap()
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* ...checks page->mapping, via PageAnon(page) call,
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* and incorrectly concludes that the page is an
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* anonymous page. Therefore, it incorrectly,
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* silently fails to set up the new anon rmap.
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*
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*
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* For other types of ZONE_DEVICE pages, migration is either
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* For other types of ZONE_DEVICE pages, migration is either
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* handled differently or not done at all, so there is no need
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* handled differently or not done at all, so there is no need
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