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Message-ID: <CALvZod6rYcJ4jimyaTTKUvXVZ4a3-G-+wqnRkV875u5npUUeAQ@mail.gmail.com>
Date: Wed, 6 Nov 2019 18:52:23 -0800
From: Shakeel Butt <shakeelb@...gle.com>
To: Johannes Weiner <hannes@...xchg.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Andrey Ryabinin <aryabinin@...tuozzo.com>,
Suren Baghdasaryan <surenb@...gle.com>,
Michal Hocko <mhocko@...e.com>, Linux MM <linux-mm@...ck.org>,
Cgroups <cgroups@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>,
Kernel Team <kernel-team@...com>
Subject: Re: [PATCH 09/11] mm: vmscan: move file exhaustion detection to the
node level
On Mon, Jun 3, 2019 at 3:08 PM Johannes Weiner <hannes@...xchg.org> wrote:
>
> When file pages are lower than the watermark on a node, we try to
> force scan anonymous pages to counter-act the balancing algorithms
> preference for new file pages when they are likely thrashing. This is
> node-level decision, but it's currently made each time we look at an
> lruvec. This is unnecessarily expensive and also a layering violation
> that makes the code harder to understand.
>
> Clean this up by making the check once per node and setting a flag in
> the scan_control.
>
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>
Reviewed-by: Shakeel Butt <shakeelb@...gle.com>
> ---
> mm/vmscan.c | 80 ++++++++++++++++++++++++++++-------------------------
> 1 file changed, 42 insertions(+), 38 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index eb535c572733..cabf94dfa92d 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -104,6 +104,9 @@ struct scan_control {
> /* One of the zones is ready for compaction */
> unsigned int compaction_ready:1;
>
> + /* The file pages on the current node are dangerously low */
> + unsigned int file_is_tiny:1;
> +
> /* Allocation order */
> s8 order;
>
> @@ -2219,45 +2222,16 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
> }
>
Unrelated to the patch. I think we need to revisit all the heuristics
that were added here over the years. get_scan_count() has become
really complicated and weird.
> /*
> - * Prevent the reclaimer from falling into the cache trap: as
> - * cache pages start out inactive, every cache fault will tip
> - * the scan balance towards the file LRU. And as the file LRU
> - * shrinks, so does the window for rotation from references.
> - * This means we have a runaway feedback loop where a tiny
> - * thrashing file LRU becomes infinitely more attractive than
> - * anon pages. Try to detect this based on file LRU size.
> + * If the system is almost out of file pages, force-scan anon.
> + * But only if there are enough inactive anonymous pages on
> + * the LRU. Otherwise, the small LRU gets thrashed.
> */
> - if (!cgroup_reclaim(sc)) {
> - unsigned long pgdatfile;
> - unsigned long pgdatfree;
> - int z;
> - unsigned long total_high_wmark = 0;
> -
> - pgdatfree = sum_zone_node_page_state(pgdat->node_id, NR_FREE_PAGES);
> - pgdatfile = node_page_state(pgdat, NR_ACTIVE_FILE) +
> - node_page_state(pgdat, NR_INACTIVE_FILE);
> -
> - for (z = 0; z < MAX_NR_ZONES; z++) {
> - struct zone *zone = &pgdat->node_zones[z];
> - if (!managed_zone(zone))
> - continue;
> -
> - total_high_wmark += high_wmark_pages(zone);
> - }
> -
> - if (unlikely(pgdatfile + pgdatfree <= total_high_wmark)) {
> - /*
> - * Force SCAN_ANON if there are enough inactive
> - * anonymous pages on the LRU in eligible zones.
> - * Otherwise, the small LRU gets thrashed.
> - */
> - if (!inactive_list_is_low(lruvec, false, sc, false) &&
> - lruvec_lru_size(lruvec, LRU_INACTIVE_ANON, sc->reclaim_idx)
> - >> sc->priority) {
> - scan_balance = SCAN_ANON;
> - goto out;
> - }
> - }
> + if (sc->file_is_tiny &&
> + !inactive_list_is_low(lruvec, false, sc, false) &&
> + lruvec_lru_size(lruvec, LRU_INACTIVE_ANON,
> + sc->reclaim_idx) >> sc->priority) {
> + scan_balance = SCAN_ANON;
> + goto out;
> }
>
> /*
> @@ -2718,6 +2692,36 @@ static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc)
> nr_reclaimed = sc->nr_reclaimed;
> nr_scanned = sc->nr_scanned;
>
> + /*
> + * Prevent the reclaimer from falling into the cache trap: as
> + * cache pages start out inactive, every cache fault will tip
> + * the scan balance towards the file LRU. And as the file LRU
> + * shrinks, so does the window for rotation from references.
> + * This means we have a runaway feedback loop where a tiny
> + * thrashing file LRU becomes infinitely more attractive than
> + * anon pages. Try to detect this based on file LRU size.
> + */
> + if (!cgroup_reclaim(sc)) {
> + unsigned long file;
> + unsigned long free;
> + int z;
> + unsigned long total_high_wmark = 0;
> +
> + free = sum_zone_node_page_state(pgdat->node_id, NR_FREE_PAGES);
> + file = node_page_state(pgdat, NR_ACTIVE_FILE) +
> + node_page_state(pgdat, NR_INACTIVE_FILE);
> +
> + for (z = 0; z < MAX_NR_ZONES; z++) {
> + struct zone *zone = &pgdat->node_zones[z];
> + if (!managed_zone(zone))
> + continue;
> +
> + total_high_wmark += high_wmark_pages(zone);
> + }
> +
> + sc->file_is_tiny = file + free <= total_high_wmark;
> + }
> +
> shrink_node_memcgs(pgdat, sc);
>
> if (reclaim_state) {
> --
> 2.21.0
>
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