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Groups > linux.kernel > #1459993
| From | Vlastimil Babka <vbabka@suse.cz> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | [PATCH v6 11/11] mm, vmscan: make compaction_ready() more accurate and readable |
| Date | 2016-08-10 23:30 +0200 |
| Message-ID | <s4Jez-29X-37@gated-at.bofh.it> (permalink) |
| References | <s4GgI-79-119@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
The compaction_ready() is used during direct reclaim for costly order
allocations to skip reclaim for zones where compaction should be attempted
instead. It's combining the standard compaction_suitable() check with its own
watermark check based on high watermark with extra gap, and the result is
confusing at best.
This patch attempts to better structure and document the checks involved.
First, compaction_suitable() can determine that the allocation should either
succeed already, or that compaction doesn't have enough free pages to proceed.
The third possibility is that compaction has enough free pages, but we still
decide to reclaim first - unless we are already above the high watermark with
gap. This does not mean that the reclaim will actually reach this watermark
during single attempt, this is rather an over-reclaim protection. So document
the code as such. The check for compaction_deferred() is removed completely, as
it in fact had no proper role here.
The result after this patch is mainly a less confusing code. We also skip some
over-reclaim in cases where the allocation should already succed.
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Michal Hocko <mhocko@suse.com>
---
mm/vmscan.c | 43 ++++++++++++++++++++-----------------------
1 file changed, 20 insertions(+), 23 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index b676b4b51db0..f9b3112e963a 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2617,38 +2617,35 @@ static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc)
}
/*
- * Returns true if compaction should go ahead for a high-order request, or
- * the high-order allocation would succeed without compaction.
+ * Returns true if compaction should go ahead for a costly-order request, or
+ * the allocation would already succeed without compaction. Return false if we
+ * should reclaim first.
*/
static inline bool compaction_ready(struct zone *zone, struct scan_control *sc)
{
unsigned long watermark;
- bool watermark_ok;
+ enum compact_result suitable;
- /*
- * Compaction takes time to run and there are potentially other
- * callers using the pages just freed. Continue reclaiming until
- * 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) + compact_gap(sc->order);
- watermark_ok = zone_watermark_ok_safe(zone, 0, watermark, sc->reclaim_idx);
-
- /*
- * If compaction is deferred, reclaim up to a point where
- * compaction will have a chance of success when re-enabled
- */
- if (compaction_deferred(zone, sc->order))
- return watermark_ok;
+ suitable = compaction_suitable(zone, sc->order, 0, sc->reclaim_idx);
+ if (suitable == COMPACT_SUCCESS)
+ /* Allocation should succeed already. Don't reclaim. */
+ return true;
+ if (suitable == COMPACT_SKIPPED)
+ /* Compaction cannot yet proceed. Do reclaim. */
+ return false;
/*
- * If compaction is not ready to start and allocation is not likely
- * to succeed without it, then keep reclaiming.
+ * Compaction is already possible, but it takes time to run and there
+ * are potentially other callers using the pages just freed. So proceed
+ * with reclaim to make a buffer of free pages available to give
+ * compaction a reasonable chance of completing and allocating the page.
+ * Note that we won't actually reclaim the whole buffer in one attempt
+ * as the target watermark in should_continue_reclaim() is lower. But if
+ * we are already above the high+gap watermark, don't reclaim at all.
*/
- if (compaction_suitable(zone, sc->order, 0, sc->reclaim_idx) == COMPACT_SKIPPED)
- return false;
+ watermark = high_wmark_pages(zone) + compact_gap(sc->order);
- return watermark_ok;
+ return zone_watermark_ok_safe(zone, 0, watermark, sc->reclaim_idx);
}
/*
--
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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