| From: "Matthew Wilcox (Oracle)" <willy@infradead.org> |
| Subject: doc: clarify refcount section by referring to folios & pages |
| Date: Wed, 11 Jan 2023 14:28:49 +0000 |
| |
| Include the rename of subpages_mapcount to _nr_pages_mapped. |
| |
| Link: https://lkml.kernel.org/r/20230111142915.1001531-4-willy@infradead.org |
| Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> |
| Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
| --- |
| |
| |
| --- a/Documentation/mm/transhuge.rst~doc-clarify-refcount-section-by-referring-to-folios-pages |
| +++ a/Documentation/mm/transhuge.rst |
| @@ -112,20 +112,20 @@ Refcounts and transparent huge pages |
| Refcounting on THP is mostly consistent with refcounting on other compound |
| pages: |
| |
| - - get_page()/put_page() and GUP operate on head page's ->_refcount. |
| + - get_page()/put_page() and GUP operate on the folio->_refcount. |
| |
| - ->_refcount in tail pages is always zero: get_page_unless_zero() never |
| succeeds on tail pages. |
| |
| - - map/unmap of PMD entry for the whole compound page increment/decrement |
| - ->compound_mapcount, stored in the first tail page of the compound page; |
| - and also increment/decrement ->subpages_mapcount (also in the first tail) |
| - by COMPOUND_MAPPED when compound_mapcount goes from -1 to 0 or 0 to -1. |
| + - map/unmap of a PMD entry for the whole THP increment/decrement |
| + folio->_entire_mapcount and also increment/decrement |
| + folio->_nr_pages_mapped by COMPOUND_MAPPED when _entire_mapcount |
| + goes from -1 to 0 or 0 to -1. |
| |
| - - map/unmap of sub-pages with PTE entry increment/decrement ->_mapcount |
| - on relevant sub-page of the compound page, and also increment/decrement |
| - ->subpages_mapcount, stored in first tail page of the compound page, when |
| - _mapcount goes from -1 to 0 or 0 to -1: counting sub-pages mapped by PTE. |
| + - map/unmap of individual pages with PTE entry increment/decrement |
| + page->_mapcount and also increment/decrement folio->_nr_pages_mapped |
| + when page->_mapcount goes from -1 to 0 or 0 to -1 as this counts |
| + the number of pages mapped by PTE. |
| |
| split_huge_page internally has to distribute the refcounts in the head |
| page to the tail pages before clearing all PG_head/tail bits from the page |
| _ |
