On Thu, Apr 18, 2013 at 08:01:05AM -0700, Johannes Weiner wrote:
> 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 */
Bah, yes, that was the intent as I was writing it. It's not what came
out my fingers. Thanks for the bashing with a clue stick.
--
Mel Gorman
SUSE Labs
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>