Re: [PATCH -mm] throttle direct reclaim when too many pages are isolated already

KAMEZAWA Hiroyuki
2009-07-16T03:21:54Z

On Wed, 15 Jul 2009 22:38:53 -0400
Rik van Riel <riel@redhat.com> wrote:

> When way too many processes go into direct reclaim, it is possible
> for all of the pages to be taken off the LRU. One result of this
> is that the next process in the page reclaim code thinks there are
> no reclaimable pages left and triggers an out of memory kill.
>
> One solution to this problem is to never let so many processes into
> the page reclaim path that the entire LRU is emptied. Limiting the
> system to only having half of each inactive list isolated for
> reclaim should be safe.
>
> Signed-off-by: Rik van Riel <riel@redhat.com>
> ---
> This patch goes on top of Kosaki's "Account the number of isolated pages"
> patch series.
>
> mm/vmscan.c | 25 +++++++++++++++++++++++++
> 1 file changed, 25 insertions(+)
>
> Index: mmotm/mm/vmscan.c
> ===================================================================
> --- mmotm.orig/mm/vmscan.c 2009-07-08 21:37:01.000000000 -0400
> +++ mmotm/mm/vmscan.c 2009-07-08 21:39:02.000000000 -0400
> @@ -1035,6 +1035,27 @@ int isolate_lru_page(struct page *page)
> }
>
> /*
> + * Are there way too many processes in the direct reclaim path already?
> + */
> +static int too_many_isolated(struct zone *zone, int file)
> +{
> + unsigned long inactive, isolated;
> +
> + if (current_is_kswapd())
> + return 0;
> +
> + if (file) {
> + inactive = zone_page_state(zone, NR_INACTIVE_FILE);
> + isolated = zone_page_state(zone, NR_ISOLATED_FILE);
> + } else {
> + inactive = zone_page_state(zone, NR_INACTIVE_ANON);
> + isolated = zone_page_state(zone, NR_ISOLATED_ANON);
> + }
> +
> + return isolated > inactive;
> +}

Why this means "too much" ?
And, could you put this check under scanning_global_lru(sc) ?

Thanks,
-Kame

> +
> +/*
> * shrink_inactive_list() is a helper for shrink_zone(). It returns the number
> * of reclaimed pages
> */
> @@ -1049,6 +1070,10 @@ static unsigned long shrink_inactive_lis
> struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
> int lumpy_reclaim = 0;
>
> + while (unlikely(too_many_isolated(zone, file))) {
> + schedule_timeout_interruptible(HZ/10);
> + }
> +
> /*
> * If we need a large contiguous chunk of memory, or have
> * trouble getting a small set of contiguous pages, we
>
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