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Groups > linux.kernel > #1459896
| From | Vlastimil Babka <vbabka@suse.cz> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | [PATCH v6 08/11] mm, compaction: create compact_gap wrapper |
| Date | 2016-08-10 22:50 +0200 |
| Message-ID | <s4IBQ-1DK-45@gated-at.bofh.it> (permalink) |
| References | <s4GgI-79-119@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
Compaction uses a watermark gap of (2UL << order) pages at various places and
it's not immediately obvious why. Abstract it through a compact_gap() wrapper
to create a single place with a thorough explanation.
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Michal Hocko <mhocko@suse.com>
---
include/linux/compaction.h | 16 ++++++++++++++++
mm/compaction.c | 7 +++----
mm/vmscan.c | 6 +++---
3 files changed, 22 insertions(+), 7 deletions(-)
diff --git a/include/linux/compaction.h b/include/linux/compaction.h
index a1fba9994728..e7f0d34a90fe 100644
--- a/include/linux/compaction.h
+++ b/include/linux/compaction.h
@@ -58,6 +58,22 @@ enum compact_result {
struct alloc_context; /* in mm/internal.h */
+/*
+ * Number of free order-0 pages that should be available above given watermark
+ * to make sure compaction has reasonable chance of not running out of free
+ * pages that it needs to isolate as migration target during its work.
+ */
+static inline unsigned long compact_gap(unsigned int order)
+{
+ /*
+ * Although all the isolations for migration are temporary, compaction
+ * may have up to 1 << order pages on its list and then try to split
+ * an (order - 1) free page. At that point, a gap of 1 << order might
+ * not be enough, so it's safer to require twice that amount.
+ */
+ return 2UL << order;
+}
+
#ifdef CONFIG_COMPACTION
extern int sysctl_compact_memory;
extern int sysctl_compaction_handler(struct ctl_table *table, int write,
diff --git a/mm/compaction.c b/mm/compaction.c
index 9bd788886b1a..ae6ecf8f8e70 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1391,11 +1391,10 @@ static enum compact_result __compaction_suitable(struct zone *zone, int order,
return COMPACT_SUCCESS;
/*
- * Watermarks for order-0 must be met for compaction. Note the 2UL.
- * This is because during migration, copies of pages need to be
- * allocated and for a short time, the footprint is higher
+ * Watermarks for order-0 must be met for compaction to be able to
+ * isolate free pages for migration targets.
*/
- watermark = low_wmark_pages(zone) + (2UL << order);
+ watermark = low_wmark_pages(zone) + compact_gap(order);
if (!__zone_watermark_ok(zone, 0, watermark, classzone_idx,
alloc_flags, wmark_target))
return COMPACT_SKIPPED;
diff --git a/mm/vmscan.c b/mm/vmscan.c
index c84784765d3a..b676b4b51db0 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2499,7 +2499,7 @@ static inline bool should_continue_reclaim(struct pglist_data *pgdat,
* If we have not reclaimed enough pages for compaction and the
* inactive lists are large enough, continue reclaiming
*/
- pages_for_compaction = (2UL << sc->order);
+ pages_for_compaction = compact_gap(sc->order);
inactive_lru_pages = node_page_state(pgdat, NR_INACTIVE_FILE);
if (get_nr_swap_pages() > 0)
inactive_lru_pages += node_page_state(pgdat, NR_INACTIVE_ANON);
@@ -2631,7 +2631,7 @@ static inline bool compaction_ready(struct zone *zone, struct scan_control *sc)
* there is a buffer of free pages available to give compaction
* a reasonable chance of completing and allocating the page
*/
- watermark = high_wmark_pages(zone) + (2UL << sc->order);
+ watermark = high_wmark_pages(zone) + compact_gap(sc->order);
watermark_ok = zone_watermark_ok_safe(zone, 0, watermark, sc->reclaim_idx);
/*
@@ -3188,7 +3188,7 @@ static bool kswapd_shrink_node(pg_data_t *pgdat,
* excessive reclaim. Assume that a process requested a high-order
* can direct reclaim/compact.
*/
- if (sc->order && sc->nr_reclaimed >= 2UL << sc->order)
+ if (sc->order && sc->nr_reclaimed >= compact_gap(sc->order))
sc->order = 0;
return sc->nr_scanned >= sc->nr_to_reclaim;
--
2.9.2
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[PATCH v6 00/11] make direct compaction more deterministic Vlastimil Babka <vbabka@suse.cz> - 2016-08-10 20:20 +0200
[PATCH v6 06/11] mm, compaction: more reliably increase direct compaction priority Vlastimil Babka <vbabka@suse.cz> - 2016-08-10 22:50 +0200
Re: [PATCH v6 06/11] mm, compaction: more reliably increase direct compaction priority Joonsoo Kim <iamjoonsoo.kim@lge.com> - 2016-08-16 08:10 +0200
Re: [PATCH v6 06/11] mm, compaction: more reliably increase direct compaction priority Vlastimil Babka <vbabka@suse.cz> - 2016-08-16 08:40 +0200
Re: [PATCH v6 06/11] mm, compaction: more reliably increase direct compaction priority Michal Hocko <mhocko@kernel.org> - 2016-08-18 11:20 +0200
Re: [PATCH v6 06/11] mm, compaction: more reliably increase direct compaction priority Vlastimil Babka <vbabka@suse.cz> - 2016-08-18 11:50 +0200
Re: [PATCH v6 06/11] mm, compaction: more reliably increase direct compaction priority Michal Hocko <mhocko@kernel.org> - 2016-08-18 12:00 +0200
[PATCH v6 09/11] mm, compaction: use proper alloc_flags in __compaction_suitable() Vlastimil Babka <vbabka@suse.cz> - 2016-08-10 22:50 +0200
[PATCH v6 01/11] mm, compaction: make whole_zone flag ignore cached scanner positions Vlastimil Babka <vbabka@suse.cz> - 2016-08-10 22:50 +0200
[PATCH v6 07/11] mm, compaction: use correct watermark when checking compaction success Vlastimil Babka <vbabka@suse.cz> - 2016-08-10 22:50 +0200
[PATCH v6 08/11] mm, compaction: create compact_gap wrapper Vlastimil Babka <vbabka@suse.cz> - 2016-08-10 22:50 +0200
Re: [PATCH v6 08/11] mm, compaction: create compact_gap wrapper Vlastimil Babka <vbabka@suse.cz> - 2016-08-16 08:20 +0200
Re: [PATCH v6 08/11] mm, compaction: create compact_gap wrapper Joonsoo Kim <iamjoonsoo.kim@lge.com> - 2016-08-16 08:40 +0200
Re: [PATCH v6 08/11] mm, compaction: create compact_gap wrapper Vlastimil Babka <vbabka@suse.cz> - 2016-08-18 14:20 +0200
Re: [PATCH v6 08/11] mm, compaction: create compact_gap wrapper Joonsoo Kim <iamjoonsoo.kim@lge.com> - 2016-08-16 08:20 +0200
[PATCH v6 03/11] mm, compaction: rename COMPACT_PARTIAL to COMPACT_SUCCESS Vlastimil Babka <vbabka@suse.cz> - 2016-08-10 22:50 +0200
Re: [PATCH v6 03/11] mm, compaction: rename COMPACT_PARTIAL to COMPACT_SUCCESS Michal Hocko <mhocko@kernel.org> - 2016-08-18 13:10 +0200
[PATCH v6 02/11] mm, compaction: cleanup unused functions Vlastimil Babka <vbabka@suse.cz> - 2016-08-10 23:30 +0200
[PATCH v6 10/11] mm, compaction: require only min watermarks for non-costly orders Vlastimil Babka <vbabka@suse.cz> - 2016-08-10 23:30 +0200
Re: [PATCH v6 10/11] mm, compaction: require only min watermarks for non-costly orders Joonsoo Kim <iamjoonsoo.kim@lge.com> - 2016-08-16 08:20 +0200
Re: [PATCH v6 10/11] mm, compaction: require only min watermarks for non-costly orders Vlastimil Babka <vbabka@suse.cz> - 2016-08-16 08:40 +0200
Re: [PATCH v6 10/11] mm, compaction: require only min watermarks for non-costly orders Joonsoo Kim <iamjoonsoo.kim@lge.com> - 2016-08-16 08:50 +0200
Re: [PATCH v6 10/11] mm, compaction: require only min watermarks for non-costly orders Vlastimil Babka <vbabka@suse.cz> - 2016-08-18 14:30 +0200
[PATCH v6 05/11] mm, compaction: add the ultimate direct compaction priority Vlastimil Babka <vbabka@suse.cz> - 2016-08-10 23:30 +0200
Re: [PATCH v6 05/11] mm, compaction: add the ultimate direct compaction priority Joonsoo Kim <iamjoonsoo.kim@lge.com> - 2016-08-16 08:00 +0200
Re: [PATCH v6 05/11] mm, compaction: add the ultimate direct compaction priority Vlastimil Babka <vbabka@suse.cz> - 2016-08-18 14:30 +0200
[PATCH v6 11/11] mm, vmscan: make compaction_ready() more accurate and readable Vlastimil Babka <vbabka@suse.cz> - 2016-08-10 23:30 +0200
[PATCH v6 04/11] mm, compaction: don't recheck watermarks after COMPACT_SUCCESS Vlastimil Babka <vbabka@suse.cz> - 2016-08-10 23:30 +0200
Re: [PATCH v6 04/11] mm, compaction: don't recheck watermarks after COMPACT_SUCCESS Joonsoo Kim <iamjoonsoo.kim@lge.com> - 2016-08-16 08:10 +0200
Re: [PATCH v6 04/11] mm, compaction: don't recheck watermarks after COMPACT_SUCCESS Vlastimil Babka <vbabka@suse.cz> - 2016-08-16 08:20 +0200
Re: [PATCH v6 04/11] mm, compaction: don't recheck watermarks after COMPACT_SUCCESS Vlastimil Babka <vbabka@suse.cz> - 2016-08-18 14:00 +0200
Re: [PATCH v6 04/11] mm, compaction: don't recheck watermarks after COMPACT_SUCCESS Michal Hocko <mhocko@kernel.org> - 2016-08-18 11:10 +0200
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