Messages in this thread Patch in this message | | | From | KOSAKI Motohiro <> | Subject | [PATCH] mm: adding comment why mark_page_accessed() would be better than pte_mkyoung() in follow_page() | Date | Fri, 13 Feb 2009 14:55:29 +0900 (JST) |
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I and hugh discussed about mark_page_accessed() in follow_page() should be change or not. and we agreed it isn't needed without adding comment.
== At first look, mark_page_accessed() in follow_page() seems a bit strange. it seems pte_mkyoung() would be better and to consist other kernel code.
However, it is intentionally. past commitlog said,
------------------------------------------------ commit 9e45f61d69be9024a2e6bef3831fb04d90fac7a8 Author: akpm <akpm> Date: Fri Aug 15 07:24:59 2003 +0000
[PATCH] Use mark_page_accessed() in follow_page()
Touching a page via follow_page() counts as a reference so we should be either setting the referenced bit in the pte or running mark_page_accessed().
Altering the pte is tricky because we haven't implemented an atomic pte_mkyoung(). And mark_page_accessed() is better anyway because it has more aging state: it can move the page onto the active list.
BKrev: 3f3c8acbplT8FbwBVGtth7QmnqWkIw ------------------------------------------------
The atomic issue is still true nowadays. adding comment help to understand code intention and it would be better.
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Signed-off-by: Hugh Dickins <hugh@veritas.com> Cc: Nick Piggin <npiggin@suse.de> --- mm/memory.c | 5 +++++ 1 file changed, 5 insertions(+)
Index: b/mm/memory.c =================================================================== --- a/mm/memory.c +++ b/mm/memory.c @@ -1151,6 +1151,11 @@ struct page *follow_page(struct vm_area_ if ((flags & FOLL_WRITE) && !pte_dirty(pte) && !PageDirty(page)) set_page_dirty(page); + /* + * pte_mkyoung() would be more correct here, but atomic care + * is needed to avoid losing dirty bit: easier to + * mark_page_accessed(). + */ mark_page_accessed(page); } unlock:
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