Hi KOSAKI,
On Sun, Apr 24, 2011 at 12:02:57PM +0900, KOSAKI Motohiro wrote:
> 2011/4/24 Minchan Kim <minchan.kim@xxxxxxxxx>:
> > In putback_lru_page, unevictable page can be changed into evictable
> > 's one while we move it among lru. So we have checked it again and
> > rescued it. But we don't check PageActive, again. It could add
> > active page into inactive list so we can see the BUG in isolate_lru_pages.
> > (But I didn't see any report because I think it's very subtle)
> >
> > It could happen in race that zap_pte_range's mark_page_accessed and
> > putback_lru_page. It's subtle but could be possible.
> >
> > Note:
> > While I review the code, I found it. So it's not real report.
> >
> > Cc: Rik van Riel <riel@xxxxxxxxxx>
> > Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
> > Cc: Hugh Dickins <hughd@xxxxxxxxxx>
> > Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> > Cc: Lee Schermerhorn <lee.schermerhorn@xxxxxx>
> > Signed-off-by: Minchan Kim <minchan.kim@xxxxxxxxx>
> > ---
> > mm/vmscan.c | 4 +++-
> > 1 files changed, 3 insertions(+), 1 deletions(-)
> >
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index b3a569f..c0cd1aa 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -562,7 +562,7 @@ int remove_mapping(struct address_space *mapping, struct page *page)
> > void putback_lru_page(struct page *page)
> > {
> > int lru;
> > - int active = !!TestClearPageActive(page);
> > + int active;
> > int was_unevictable = PageUnevictable(page);
> >
> > VM_BUG_ON(PageLRU(page));
> > @@ -571,6 +571,7 @@ redo:
> > ClearPageUnevictable(page);
> >
> > if (page_evictable(page, NULL)) {
> > + active = !!TestClearPageActive(page);
> > /*
> > * For evictable pages, we can use the cache.
> > * In event of a race, worst case is we end up with an
> > @@ -584,6 +585,7 @@ redo:
> > * Put unevictable pages directly on zone's unevictable
> > * list.
> > */
> > + ClearPageActive(page);
> > lru = LRU_UNEVICTABLE;
> > add_page_to_unevictable_list(page);
>
> I think we forgot 'goto redo' case. following patch is better?
>
> ------------------------------------------------
> if (page_evictable(page, NULL)) {
> /*
> * For evictable pages, we can use the cache.
> * In event of a race, worst case is we end up with an
> * unevictable page on [in]active list.
> * We know how to handle that.
> */
> lru = active + page_lru_base_type(page);
> + if (active)
> + SetPageActive(page);
> lru_cache_add_lru(page, lru);
PageActive is reset by lru_cache_add_lru so it's meaningless.
BTW, please ignore this patch. :)
I think LRU status of isolated page cannot be changed.
Thanks for the review.
--
Kind regards,
Minchan Kim
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxxx For more info on Linux MM,
see: http://www.linux-mm.org/ .
Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>