On Fri, 17 Aug 2012 15:14:32 +0100
Mel Gorman <mgorman@xxxxxxx> wrote:
> 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.
>
> ...
>
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1743,6 +1743,7 @@ static inline bool should_continue_reclaim(struct lruvec *lruvec,
> {
> unsigned long pages_for_compaction;
> unsigned long inactive_lru_pages;
> + struct zone *zone;
>
> /* If not in reclaim/compaction mode, stop */
> if (!in_reclaim_compaction(sc))
> @@ -1776,6 +1777,15 @@ static inline bool should_continue_reclaim(struct lruvec *lruvec,
> * inactive lists are large enough, continue reclaiming
> */
> pages_for_compaction = (2UL << sc->order);
> +
> + /*
> + * If compaction is deferred for sc->order then scale the number of
> + * pages reclaimed based on the number of consecutive allocation
> + * failures
> + */
> + zone = lruvec_zone(lruvec);
> + if (zone->compact_order_failed <= sc->order)
> + pages_for_compaction <<= zone->compact_defer_shift;
> 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);
y'know, allnoconfig builds are really fast.
mm/vmscan.c: In function 'should_continue_reclaim':
mm/vmscan.c:1787: error: 'struct zone' has no member named 'compact_order_failed'
mm/vmscan.c:1788: error: 'struct zone' has no member named 'compact_defer_shift'
This fix seems a rather overly ornate way of avoiding an ifdef :(
From: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Subject: mm-vmscan-scale-number-of-pages-reclaimed-by-reclaim-compaction-based-on-failures-fix
fix build
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/vmscan.c | 33 ++++++++++++++++++++++++---------
1 file changed, 24 insertions(+), 9 deletions(-)
diff -puN mm/vmscan.c~mm-vmscan-scale-number-of-pages-reclaimed-by-reclaim-compaction-based-on-failures-fix mm/vmscan.c
--- a/mm/vmscan.c~mm-vmscan-scale-number-of-pages-reclaimed-by-reclaim-compaction-based-on-failures-fix
+++ a/mm/vmscan.c
@@ -1729,6 +1729,28 @@ static bool in_reclaim_compaction(struct
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
@@ -1743,7 +1765,6 @@ static inline bool should_continue_recla
{
unsigned long pages_for_compaction;
unsigned long inactive_lru_pages;
- struct zone *zone;
/* If not in reclaim/compaction mode, stop */
if (!in_reclaim_compaction(sc))
@@ -1778,14 +1799,8 @@ static inline bool should_continue_recla
*/
pages_for_compaction = (2UL << sc->order);
- /*
- * If compaction is deferred for sc->order then scale the number of
- * pages reclaimed based on the number of consecutive allocation
- * failures
- */
- zone = lruvec_zone(lruvec);
- if (zone->compact_order_failed <= sc->order)
- pages_for_compaction <<= zone->compact_defer_shift;
+ 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);
_
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