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Diffstat (limited to 'Documentation/mm/transhuge.rst')
| -rw-r--r-- | Documentation/mm/transhuge.rst | 26 |
1 files changed, 12 insertions, 14 deletions
diff --git a/Documentation/mm/transhuge.rst b/Documentation/mm/transhuge.rst index ec3dc5b04226..9a607059ea11 100644 --- a/Documentation/mm/transhuge.rst +++ b/Documentation/mm/transhuge.rst @@ -1,5 +1,3 @@ -.. _transhuge: - ============================ Transparent Hugepage Support ============================ @@ -112,20 +110,20 @@ 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 @@ -153,8 +151,8 @@ clear where references should go after split: it will stay on the head page. Note that split_huge_pmd() doesn't have any limitations on refcounting: pmd can be split at any point and never fails. -Partial unmap and deferred_split_huge_page() -============================================ +Partial unmap and deferred_split_folio() +======================================== Unmapping part of THP (with munmap() or other way) is not going to free memory immediately. Instead, we detect that a subpage of THP is not in use @@ -166,6 +164,6 @@ the place where we can detect partial unmap. It also might be counterproductive since in many cases partial unmap happens during exit(2) if a THP crosses a VMA boundary. -The function deferred_split_huge_page() is used to queue a page for splitting. +The function deferred_split_folio() is used to queue a folio for splitting. The splitting itself will happen when we get memory pressure via shrinker interface. |