mm: vmscan: scale number of pages reclaimed by reclaim/compaction based on failures

If allocation fails after compaction then compaction may be deferred for
a number of allocation attempts.  If there are subsequent failures,
compact_defer_shift is increased to defer for longer periods.  This
patch uses that information to scale the number of pages reclaimed with
compact_defer_shift until allocations succeed again.  The rationale is
that reclaiming the normal number of pages still allowed compaction to
fail and its success depends on the number of pages.  If it's failing,
reclaim more pages until it succeeds again.

Note that this is not implying that VM reclaim is not reclaiming enough
pages or that its logic is broken.  try_to_free_pages() always asks for
SWAP_CLUSTER_MAX pages to be reclaimed regardless of order and that is
what it does.  Direct reclaim stops normally with this check.

	if (sc->nr_reclaimed >= sc->nr_to_reclaim)
		goto out;

should_continue_reclaim delays when that check is made until a minimum
number of pages for reclaim/compaction are reclaimed.  It is possible
that this patch could instead set nr_to_reclaim in try_to_free_pages()
and drive it from there but that's behaves differently and not
necessarily for the better.  If driven from do_try_to_free_pages(), it
is also possible that priorities will rise.

When they reach DEF_PRIORITY-2, it will also start stalling and setting
pages for immediate reclaim which is more disruptive than not desirable
in this case.  That is a more wide-reaching change that could cause
another regression related to THP requests causing interactive jitter.

[akpm@linux-foundation.org: fix build]
Signed-off-by: Mel Gorman <mgorman@suse.de>
Acked-by: Rik van Riel <riel@redhat.com>
Reviewed-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 99b434b674c02b4099bcfe58632ad56e183801fd..f6fdae7a8d4c069e601c32b2179f2ff1b365d402 100644 (file)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1729,6 +1729,28 @@ static bool in_reclaim_compaction(struct scan_control *sc)
        return false;
 }
 
+#ifdef CONFIG_COMPACTION
+/*
+ * If compaction is deferred for sc->order then scale the number of pages
+ * reclaimed based on the number of consecutive allocation failures
+ */
+static unsigned long scale_for_compaction(unsigned long pages_for_compaction,
+                       struct lruvec *lruvec, struct scan_control *sc)
+{
+       struct zone *zone = lruvec_zone(lruvec);
+
+       if (zone->compact_order_failed <= sc->order)
+               pages_for_compaction <<= zone->compact_defer_shift;
+       return pages_for_compaction;
+}
+#else
+static unsigned long scale_for_compaction(unsigned long pages_for_compaction,
+                       struct lruvec *lruvec, struct scan_control *sc)
+{
+       return pages_for_compaction;
+}
+#endif
+
 /*
  * Reclaim/compaction is used for high-order allocation requests. It reclaims
  * order-0 pages before compacting the zone. should_continue_reclaim() returns
@@ -1776,6 +1798,9 @@ static inline bool should_continue_reclaim(struct lruvec *lruvec,
         * inactive lists are large enough, continue reclaiming
         */
        pages_for_compaction = (2UL << sc->order);
+
+       pages_for_compaction = scale_for_compaction(pages_for_compaction,
+                                                   lruvec, sc);
        inactive_lru_pages = get_lru_size(lruvec, LRU_INACTIVE_FILE);
        if (nr_swap_pages > 0)
                inactive_lru_pages += get_lru_size(lruvec, LRU_INACTIVE_ANON);