On Wed, 9 Jan 2013 15:21:14 +0900
Minchan Kim <minchan@xxxxxxxxxx> wrote:
> If laptop_mode is enable, VM try to avoid I/O for saving the power.
> But if there isn't reclaimable memory without I/O, we should do I/O
> for preventing unnecessary OOM kill although we sacrifices power.
>
> One of example is that we are out of page cache. Remained one is
> only anonymous pages, for swapping out, we needs may_writepage = 1.
>
> Reported-by: Luigi Semenzato <semenzato@xxxxxxxxxx>
> Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
> ---
> mm/vmscan.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 439cc47..624c816 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1728,6 +1728,12 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
> free = zone_page_state(zone, NR_FREE_PAGES);
> if (unlikely(file + free <= high_wmark_pages(zone))) {
> scan_balance = SCAN_ANON;
> + /*
> + * From now on, we have to swap out
> + * for peventing OOM kill although
> + * we sacrifice power consumption.
> + */
> + sc->may_writepage = 1;
> goto out;
> }
> }
This is pretty ugly. get_scan_count() is, as its name implies, an
idempotent function which inspects the state of things and returns a
result. As such, it has no business going in and altering the state of
the scan_control.
We have code in both direct reclaim and in kswapd to set may_writepage
if vmscan is getting into trouble. I don't see why adding another
instance is necessary if the existing instances are working correctly.
(Is it correct that __zone_reclaim() ignores laptop_mode?)
I have a feeling that laptop mode has bitrotted and these patches are
kinda hacking around as-yet-not-understood failures...
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