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| author | KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> | 2009-03-31 15:19:37 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2009-04-01 08:59:12 -0700 |
| commit | bd775c42ea5f7c766d03a287083837cf05e7e738 (patch) | |
| tree | 40084f399068bed56c3061afd5e1175c679160df /mm/memory.c | |
| parent | 9786bf841da57fac3457a1dac41acb4c1f2eced6 (diff) | |
| download | lwn-bd775c42ea5f7c766d03a287083837cf05e7e738.tar.gz lwn-bd775c42ea5f7c766d03a287083837cf05e7e738.zip | |
mm: add comment why mark_page_accessed() would be better than pte_mkyoung() in follow_page()
At first look, mark_page_accessed() in follow_page() seems a bit strange.
It seems pte_mkyoung() would be better consistent with other kernel code.
However, it is intentional. The commit log 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.
[akpm@linux-foundation.org: clarify text]
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Cc: Nick Piggin <npiggin@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/memory.c')
| -rw-r--r-- | mm/memory.c | 5 |
1 files changed, 5 insertions, 0 deletions
diff --git a/mm/memory.c b/mm/memory.c index 0017111214c5..5b4ad5e4f98d 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -1151,6 +1151,11 @@ struct page *follow_page(struct vm_area_struct *vma, unsigned long address, 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 the dirty bit: it is easier to use + * mark_page_accessed(). + */ mark_page_accessed(page); } unlock: |