On Mon 13-05-13 09:12:33, Mel Gorman wrote:
> Simplistically, the anon and file LRU lists are scanned proportionally
> depending on the value of vm.swappiness although there are other factors
> taken into account by get_scan_count(). The patch "mm: vmscan: Limit
> the number of pages kswapd reclaims" limits the number of pages kswapd
> reclaims but it breaks this proportional scanning and may evenly shrink
> anon/file LRUs regardless of vm.swappiness.
>
> This patch preserves the proportional scanning and reclaim. It does mean
> that kswapd will reclaim more than requested but the number of pages will
> be related to the high watermark.
>
> [mhocko@xxxxxxx: Correct proportional reclaim for memcg and simplify]
> [kamezawa.hiroyu@xxxxxxxxxxxxxx: Recalculate scan based on target]
> [hannes@xxxxxxxxxxx: Account for already scanned pages properly]
> Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
> Acked-by: Rik van Riel <riel@xxxxxxxxxx>
active vs. inactive might get skewed a bit AFAICS because both of them
are zeroed but file vs. anon should be scanned proportionally based on
swappiness now which sounds like it is good enough.
Reviewed-by: Michal Hocko <mhocko@xxxxxxx>
> ---
> mm/vmscan.c | 67 +++++++++++++++++++++++++++++++++++++++++++++++++++++--------
> 1 file changed, 59 insertions(+), 8 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index cdbc069..26ad67f 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1822,17 +1822,25 @@ out:
> static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
> {
> unsigned long nr[NR_LRU_LISTS];
> + unsigned long targets[NR_LRU_LISTS];
> unsigned long nr_to_scan;
> enum lru_list lru;
> unsigned long nr_reclaimed = 0;
> unsigned long nr_to_reclaim = sc->nr_to_reclaim;
> struct blk_plug plug;
> + bool scan_adjusted = false;
>
> get_scan_count(lruvec, sc, nr);
>
> + /* Record the original scan target for proportional adjustments later */
> + memcpy(targets, nr, sizeof(nr));
> +
> blk_start_plug(&plug);
> while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] ||
> nr[LRU_INACTIVE_FILE]) {
> + unsigned long nr_anon, nr_file, percentage;
> + unsigned long nr_scanned;
> +
> for_each_evictable_lru(lru) {
> if (nr[lru]) {
> nr_to_scan = min(nr[lru], SWAP_CLUSTER_MAX);
> @@ -1842,17 +1850,60 @@ static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
> lruvec, sc);
> }
> }
> +
> + if (nr_reclaimed < nr_to_reclaim || scan_adjusted)
> + continue;
> +
> /*
> - * On large memory systems, scan >> priority can become
> - * really large. This is fine for the starting priority;
> - * we want to put equal scanning pressure on each zone.
> - * However, if the VM has a harder time of freeing pages,
> - * with multiple processes reclaiming pages, the total
> - * freeing target can get unreasonably large.
> + * For global direct reclaim, reclaim only the number of pages
> + * requested. Less care is taken to scan proportionally as it
> + * is more important to minimise direct reclaim stall latency
> + * than it is to properly age the LRU lists.
> */
> - if (nr_reclaimed >= nr_to_reclaim &&
> - sc->priority < DEF_PRIORITY)
> + if (global_reclaim(sc) && !current_is_kswapd())
> break;
> +
> + /*
> + * For kswapd and memcg, reclaim at least the number of pages
> + * requested. Ensure that the anon and file LRUs shrink
> + * proportionally what was requested by get_scan_count(). We
> + * stop reclaiming one LRU and reduce the amount scanning
> + * proportional to the original scan target.
> + */
> + nr_file = nr[LRU_INACTIVE_FILE] + nr[LRU_ACTIVE_FILE];
> + nr_anon = nr[LRU_INACTIVE_ANON] + nr[LRU_ACTIVE_ANON];
> +
> + if (nr_file > nr_anon) {
> + unsigned long scan_target = targets[LRU_INACTIVE_ANON] +
> + targets[LRU_ACTIVE_ANON] + 1;
> + lru = LRU_BASE;
> + percentage = nr_anon * 100 / scan_target;
> + } else {
> + unsigned long scan_target = targets[LRU_INACTIVE_FILE] +
> + targets[LRU_ACTIVE_FILE] + 1;
> + lru = LRU_FILE;
> + percentage = nr_file * 100 / scan_target;
> + }
> +
> + /* Stop scanning the smaller of the LRU */
> + nr[lru] = 0;
> + nr[lru + LRU_ACTIVE] = 0;
> +
> + /*
> + * Recalculate the other LRU scan count based on its original
> + * scan target and the percentage scanning already complete
> + */
> + lru = (lru == LRU_FILE) ? LRU_BASE : LRU_FILE;
> + nr_scanned = targets[lru] - nr[lru];
> + nr[lru] = targets[lru] * (100 - percentage) / 100;
> + nr[lru] -= min(nr[lru], nr_scanned);
> +
> + lru += LRU_ACTIVE;
> + nr_scanned = targets[lru] - nr[lru];
> + nr[lru] = targets[lru] * (100 - percentage) / 100;
> + nr[lru] -= min(nr[lru], nr_scanned);
> +
> + scan_adjusted = true;
> }
> blk_finish_plug(&plug);
> sc->nr_reclaimed += nr_reclaimed;
> --
> 1.8.1.4
>
--
Michal Hocko
SUSE Labs
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