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Date: Wed, 10 Dec 2014 15:46:32 +0900
From: Joonsoo Kim <iamjoonsoo.kim@....com>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Mel Gorman <mgorman@...e.de>,
David Rientjes <rientjes@...gle.com>,
Rik van Riel <riel@...hat.com>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] mm/compaction: enhance compaction finish condition
On Mon, Dec 08, 2014 at 10:34:05AM +0100, Vlastimil Babka wrote:
> On 12/08/2014 08:16 AM, Joonsoo Kim wrote:
> >Compaction has anti fragmentation algorithm. It is that freepage
> >should be more than pageblock order to finish the compaction if we don't
> >find any freepage in requested migratetype buddy list. This is for
> >mitigating fragmentation, but, it is a lack of migratetype consideration
> >and too excessive.
> >
> >At first, it doesn't consider migratetype so there would be false positive
> >on compaction finish decision. For example, if allocation request is
> >for unmovable migratetype, freepage in CMA migratetype doesn't help that
> >allocation, so compaction should not be stopped. But, current logic
> >considers it as compaction is no longer needed and stop the compaction.
> >
> >Secondly, it is too excessive. We can steal freepage from other migratetype
> >and change pageblock migratetype on more relaxed conditions. In page
> >allocator, there is another conditions that can succeed to steal without
> >introducing fragmentation.
> >
> >To solve these problems, this patch borrows anti fragmentation logic from
> >page allocator. It will reduce premature compaction finish in some cases
> >and reduce excessive compaction work.
> >
> >stress-highalloc test in mmtests with non movable order 7 allocation shows
> >in allocation success rate on phase 1 and compaction success rate.
> >
> >Allocation success rate on phase 1 (%)
> >57.00 : 63.67
> >
> >Compaction success rate (Compaction success * 100 / Compaction stalls, %)
> >28.94 : 35.13
> >
> >Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
> >---
> > include/linux/mmzone.h | 3 +++
> > mm/compaction.c | 31 +++++++++++++++++++++++++++++--
> > mm/internal.h | 1 +
> > mm/page_alloc.c | 5 ++---
> > 4 files changed, 35 insertions(+), 5 deletions(-)
> >
> >diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> >index 2f0856d..87f5bb5 100644
> >--- a/include/linux/mmzone.h
> >+++ b/include/linux/mmzone.h
> >@@ -63,6 +63,9 @@ enum {
> > MIGRATE_TYPES
> > };
> >
> >+#define FALLBACK_MIGRATETYPES (4)
> >+extern int fallbacks[MIGRATE_TYPES][FALLBACK_MIGRATETYPES];
> >+
> > #ifdef CONFIG_CMA
> > # define is_migrate_cma(migratetype) unlikely((migratetype) == MIGRATE_CMA)
> > #else
> >diff --git a/mm/compaction.c b/mm/compaction.c
> >index 1a5f465..2fd5f79 100644
> >--- a/mm/compaction.c
> >+++ b/mm/compaction.c
> >@@ -1054,6 +1054,30 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone,
> > return cc->nr_migratepages ? ISOLATE_SUCCESS : ISOLATE_NONE;
> > }
> >
> >+static bool can_steal_fallbacks(struct free_area *area,
> >+ unsigned int order, int migratetype)
> >+{
> >+ int i;
> >+ int fallback_mt;
> >+
> >+ if (area->nr_free == 0)
> >+ return false;
> >+
> >+ for (i = 0; i < FALLBACK_MIGRATETYPES; i++) {
> >+ fallback_mt = fallbacks[migratetype][i];
> >+ if (fallback_mt == MIGRATE_RESERVE)
> >+ break;
> >+
> >+ if (list_empty(&area->free_list[fallback_mt]))
> >+ continue;
> >+
> >+ if (can_steal_freepages(order, migratetype, fallback_mt))
> >+ return true;
> >+ }
> >+
> >+ return false;
> >+}
> >+
> > static int __compact_finished(struct zone *zone, struct compact_control *cc,
> > const int migratetype)
> > {
> >@@ -1104,8 +1128,11 @@ static int __compact_finished(struct zone *zone, struct compact_control *cc,
> > if (!list_empty(&area->free_list[migratetype]))
> > return COMPACT_PARTIAL;
> >
> >- /* Job done if allocation would set block type */
> >- if (order >= pageblock_order && area->nr_free)
>
> So, can_steal_fallbacks() -> can_steal_freepages() is quite involved
> way if in the end we just realize that order >= pageblock_order and
> we are stealing whole pageblock. Given that often compaction is done
> for THP, it would be better to check order >= pageblock_order and
> handle it upfront. This goes together with my comments on previous
> patch that order >= pageblock_order is better handled separately.
I'd like to keep this order check in can_steal_freepages(). At first, we
should first check migratetype before order checking. If high order page
is on CMA, we can't steal it. Secondly, I think that maintaining well
defined function to check whether we can steal or not is better than
separating logic. It would help future maintanance.
Thanks.
>
> >+ /*
> >+ * Job done if allocation would steal freepages from
> >+ * other migratetype buddy lists.
> >+ */
> >+ if (can_steal_fallbacks(area, order, migratetype))
> > return COMPACT_PARTIAL;
> > }
> >
> >diff --git a/mm/internal.h b/mm/internal.h
> >index efad241..7028d83 100644
> >--- a/mm/internal.h
> >+++ b/mm/internal.h
> >@@ -179,6 +179,7 @@ unsigned long
> > isolate_migratepages_range(struct compact_control *cc,
> > unsigned long low_pfn, unsigned long end_pfn);
> >
> >+bool can_steal_freepages(unsigned int order, int start_mt, int fallback_mt);
> > #endif
> >
> > /*
> >diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> >index 7b4c9aa..dcb8523 100644
> >--- a/mm/page_alloc.c
> >+++ b/mm/page_alloc.c
> >@@ -1031,7 +1031,7 @@ struct page *__rmqueue_smallest(struct zone *zone, unsigned int order,
> > * This array describes the order lists are fallen back to when
> > * the free lists for the desirable migrate type are depleted
> > */
> >-static int fallbacks[MIGRATE_TYPES][4] = {
> >+int fallbacks[MIGRATE_TYPES][FALLBACK_MIGRATETYPES] = {
> > [MIGRATE_UNMOVABLE] = { MIGRATE_RECLAIMABLE, MIGRATE_MOVABLE, MIGRATE_RESERVE },
> > [MIGRATE_RECLAIMABLE] = { MIGRATE_UNMOVABLE, MIGRATE_MOVABLE, MIGRATE_RESERVE },
> > #ifdef CONFIG_CMA
> >@@ -1161,8 +1161,7 @@ static void try_to_steal_freepages(struct zone *zone, struct page *page,
> > }
> > }
> >
> >-static bool can_steal_freepages(unsigned int order,
> >- int start_mt, int fallback_mt)
> >+bool can_steal_freepages(unsigned int order, int start_mt, int fallback_mt)
> > {
> > /*
> > * When borrowing from MIGRATE_CMA, we need to release the excess
> >
>
> --
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