On Thu, Jun 02, 2011 at 08:23:02PM +0200, Andrea Arcangeli wrote:
> On Tue, May 31, 2011 at 11:38:30PM +0900, Minchan Kim wrote:
> > > Yes. You find a new BUG.
> > > It seems to be related to this problem but it should be solved although
> >
> > typo : It doesn't seem to be.
>
> This should fix it, but I doubt it matters for this problem.
>
> ===
> Subject: mm: no page_count without a page pin
>
> From: Andrea Arcangeli <aarcange@xxxxxxxxxx>
>
> It's unsafe to run page_count during the physical pfn scan.
>
> Signed-off-by: Andrea Arcangeli <aarcange@xxxxxxxxxx>
> ---
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index faa0a08..e41e78a 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1124,8 +1124,18 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
> nr_lumpy_dirty++;
> scan++;
> } else {
> - /* the page is freed already. */
> - if (!page_count(cursor_page))
> + /*
> + * We can't use page_count() as that
> + * requires compound_head and we don't
> + * have a pin on the page here. If a
> + * page is tail, we may or may not
> + * have isolated the head, so assume
> + * it's not free, it'd be tricky to
Isn't it rather aggressive?
I think cursor page is likely to be PageTail rather than PageHead.
Could we handle it simply with below code?
get_page(cursor_page)
/* The page is freed already */
if (1 == page_count(cursor_page)) {
put_page(cursor_page)
continue;
}
put_page(cursor_page);
> + * track the head status without a
> + * page pin.
> + */
> + if (!PageTail(cursor_page) &&
> + !atomic_read(&cursor_page->_count))
> continue;
> break;
> }
--
Kind regards
Minchan Kim
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