On Thu, Apr 11, 2013 at 08:57:50PM +0100, Mel Gorman wrote:
> @@ -1841,17 +1848,58 @@ 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[lru] = targets[lru] * (100 - percentage) / 100;
> + nr[lru] -= min(nr[lru], (targets[lru] - nr[lru]));
This doesn't seem right. Say percentage is 60, then
nr[lru] = targets[lru] * (100 - percentage) / 100;
sets nr[lru] to 40% of targets[lru], and so in
nr[lru] -= min(nr[lru], (targets[lru] - nr[lru]));
targets[lru] - nr[lru] is 60% of targets[lru], making it bigger than
nr[lru], which is in turn subtracted from itself, i.e. it leaves the
remaining type at 0 if >= 50% of the other type were scanned, and at
half of the inverted scan percentage if less than 50% were scanned.
Would this be more sensible?
already_scanned = targets[lru] - nr[lru];
nr[lru] = targets[lru] * percentage / 100; /* adjusted original target */
nr[lru] -= min(nr[lru], already_scanned); /* minus work already done */
--
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