On Tue, Dec 27, 2016 at 04:55:33PM +0100, Michal Hocko wrote:
> Hi,
> could you try to run with the following patch on top of the previous
> one? I do not think it will make a large change in your workload but
> I think we need something like that so some testing under which is known
> to make a high lowmem pressure would be really appreciated. If you have
> more time to play with it then running with and without the patch with
> mm_vmscan_direct_reclaim_{start,end} tracepoints enabled could tell us
> whether it make any difference at all.
>
> I would also appreciate if Mel and Johannes had a look at it. I am not
> yet sure whether we need the same thing for anon/file balancing in
> get_scan_count. I suspect we need but need to think more about that.
>
> Thanks a lot again!
> ---
> From b51f50340fe9e40b68be198b012f8ab9869c1850 Mon Sep 17 00:00:00 2001
> From: Michal Hocko <mho...@suse.com>
> Date: Tue, 27 Dec 2016 16:28:44 +0100
> Subject: [PATCH] mm, vmscan: consider eligible zones in get_scan_count
>
> get_scan_count considers the whole node LRU size when
> - doing SCAN_FILE due to many page cache inactive pages
> - calculating the number of pages to scan
>
> in both cases this might lead to unexpected behavior especially on 32b
> systems where we can expect lowmem memory pressure very often.
>
> A large highmem zone can easily distort SCAN_FILE heuristic because
> there might be only few file pages from the eligible zones on the node
> lru and we would still enforce file lru scanning which can lead to
> trashing while we could still scan anonymous pages.
Nit:
It doesn't make thrashing because isolate_lru_pages filter out them
but I agree it makes pointless CPU burning to find eligible pages.
>
> The later use of lruvec_lru_size can be problematic as well. Especially
> when there are not many pages from the eligible zones. We would have to
> skip over many pages to find anything to reclaim but shrink_node_memcg
> would only reduce the remaining number to scan by SWAP_CLUSTER_MAX
> at maximum. Therefore we can end up going over a large LRU many times
> without actually having chance to reclaim much if anything at all. The
> closer we are out of memory on lowmem zone the worse the problem will
> be.
>
> Signed-off-by: Michal Hocko <mho...@suse.com>
> ---
> mm/vmscan.c | 30 ++++++++++++++++++++++++++++--
> 1 file changed, 28 insertions(+), 2 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index c98b1a585992..785b4d7fb8a0 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -252,6 +252,32 @@ unsigned long lruvec_zone_lru_size(struct lruvec
> *lruvec, enum lru_list lru, int
> }
>
> /*
> + * Return the number of pages on the given lru which are eligibne for the
eligible
> + * given zone_idx
> + */
> +static unsigned long lruvec_lru_size_zone_idx(struct lruvec *lruvec,
> + enum lru_list lru, int zone_idx)
Nit:
Although there is a comment, function name is rather confusing when I compared
it with lruvec_zone_lru_size.
lruvec_eligible_zones_lru_size is better?
> +{
> + struct pglist_data *pgdat = lruvec_pgdat(lruvec);
> + unsigned long lru_size;
> + int zid;
> +
> + lru_size = lruvec_lru_size(lruvec, lru);
> + for (zid = zone_idx + 1; zid < MAX_NR_ZONES; zid++) {
> + struct zone *zone = &pgdat->node_zones[zid];
> + unsigned long size;
> +
> + if (!managed_zone(zone))
> + continue;
> +
> + size = lruvec_zone_lru_size(lruvec, lru, zid);
> + lru_size -= min(size, lru_size);
> + }
> +
> + return lru_size;
> +}
> +
> +/*
> * Add a shrinker callback to be called from the vm.
> */
> int register_shrinker(struct shrinker *shrinker)
> @@ -2207,7 +2233,7 @@ static void get_scan_count(struct lruvec *lruvec,
> struct mem_cgroup *memcg,
> * system is under heavy pressure.
> */
> if (!inactive_list_is_low(lruvec, true, sc) &&
> - lruvec_lru_size(lruvec, LRU_INACTIVE_FILE) >> sc->priority) {
> + lruvec_lru_size_zone_idx(lruvec, LRU_INACTIVE_FILE,
> sc->reclaim_idx) >> sc->priority) {
> scan_balance = SCAN_FILE;
> goto out;
> }
> @@ -2274,7 +2300,7 @@ static void get_scan_count(struct lruvec *lruvec,
> struct mem_cgroup *memcg,
> unsigned long size;
> unsigned long scan;
>
> - size = lruvec_lru_size(lruvec, lru);
> + size = lruvec_lru_size_zone_idx(lruvec, lru,
> sc->reclaim_idx);
> scan = size >> sc->priority;
>
> if (!scan && pass && force_scan)
> --
> 2.10.2
Nit:
With this patch, inactive_list_is_low can use lruvec_lru_size_zone_idx rather
than
own custom calculation to filter out non-eligible pages.
Anyway, I think this patch does right things so I suppose this.
Acked-by: Minchan Kim <minc...@kernel.org>
