Messages in this thread Patch in this message | | | Date | Tue, 17 Feb 2015 10:46:04 +0100 | From | Vlastimil Babka <> | Subject | Re: [PATCH v4 3/3] mm/compaction: enhance compaction finish condition |
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On 02/12/2015 08:15 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, there is a lack of migratetype > consideration and it is too excessive compared to page allocator's anti > fragmentation algorithm. > > Not considering migratetype would cause premature finish of compaction. > For example, if allocation request is for unmovable migratetype, > freepage with CMA migratetype doesn't help that allocation and > compaction should not be stopped. But, current logic regards this > situation as compaction is no longer needed, so finish the compaction. > > Secondly, condition is too excessive compared to page allocator's logic. > We can steal freepage from other migratetype and change pageblock > migratetype on more relaxed conditions in page allocator. This is designed > to prevent fragmentation and we can use it here. Imposing hard constraint > only to the compaction doesn't help much in this case since page allocator > would cause fragmentation again. > > 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 > considerable increase of compaction success rate. > > Compaction success rate (Compaction success * 100 / Compaction stalls, %) > 31.82 : 42.20 > > I tested it on non-reboot 5 runs stress-highalloc benchmark and found that > there is no more degradation on allocation success rate than before. That > roughly means that this patch doesn't result in more fragmentations. > > Vlastimil suggests additional idea that we only test for fallbacks > when migration scanner has scanned a whole pageblock. It looked good for > fragmentation because chance of stealing increase due to making more > free pages in certain pageblock. So, I tested it, but, it results in > decreased compaction success rate, roughly 38.00. I guess the reason that > if system is low memory condition, watermark check could be failed due to > not enough order 0 free page and so, sometimes, we can't reach a fallback > check although migrate_pfn is aligned to pageblock_nr_pages. I can insert > code to cope with this situation but it makes code more complicated so > I don't include his idea at this patch.
Hm that's weird. I'll try to investigate this later. Meanwhile it can stay as it is.
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
But you'll need to fix:
> --- > mm/compaction.c | 14 ++++++++++++-- > mm/internal.h | 2 ++ > mm/page_alloc.c | 19 ++++++++++++++----- > 3 files changed, 28 insertions(+), 7 deletions(-) > > diff --git a/mm/compaction.c b/mm/compaction.c > index 782772d..d40c426 100644 > --- a/mm/compaction.c > +++ b/mm/compaction.c > @@ -1170,13 +1170,23 @@ static int __compact_finished(struct zone *zone, struct compact_control *cc, > /* Direct compactor: Is a suitable page free? */ > for (order = cc->order; order < MAX_ORDER; order++) { > struct free_area *area = &zone->free_area[order]; > + bool can_steal; > > /* Job done if page is free of the right migratetype */ > 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) > + /* MIGRATE_MOVABLE can fallback on MIGRATE_CMA */ > + if (migratetype == MIGRATE_MOVABLE && > + !list_empty(&area->free_list[MIGRATE_CMA]))
This won't compile with !CONFIG_CMA, right? I recall pointing it on v3 already (or something similar elsewhere).
> + return COMPACT_PARTIAL; > + > + /* > + * Job done if allocation would steal freepages from > + * other migratetype buddy lists. > + */ > + if (find_suitable_fallback(area, order, migratetype, > + true, &can_steal) != -1) > return COMPACT_PARTIAL; > } > > diff --git a/mm/internal.h b/mm/internal.h > index c4d6c9b..9640650 100644 > --- a/mm/internal.h > +++ b/mm/internal.h > @@ -200,6 +200,8 @@ isolate_freepages_range(struct compact_control *cc, > unsigned long > isolate_migratepages_range(struct compact_control *cc, > unsigned long low_pfn, unsigned long end_pfn); > +int find_suitable_fallback(struct free_area *area, unsigned int order, > + int migratetype, bool only_stealable, bool *can_steal); > > #endif > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 64a4974..95654f9 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -1191,9 +1191,14 @@ static void steal_suitable_fallback(struct zone *zone, struct page *page, > set_pageblock_migratetype(page, start_type); > } > > -/* Check whether there is a suitable fallback freepage with requested order. */ > -static int find_suitable_fallback(struct free_area *area, unsigned int order, > - int migratetype, bool *can_steal) > +/* > + * Check whether there is a suitable fallback freepage with requested order. > + * If only_stealable is true, this function returns fallback_mt only if > + * we can steal other freepages all together. This would help to reduce > + * fragmentation due to mixed migratetype pages in one pageblock. > + */ > +int find_suitable_fallback(struct free_area *area, unsigned int order, > + int migratetype, bool only_stealable, bool *can_steal) > { > int i; > int fallback_mt; > @@ -1213,7 +1218,11 @@ static int find_suitable_fallback(struct free_area *area, unsigned int order, > if (can_steal_fallback(order, migratetype)) > *can_steal = true; > > - return fallback_mt; > + if (!only_stealable) > + return fallback_mt; > + > + if (*can_steal) > + return fallback_mt;
Why not just single if (!only_stealable || *can_steal)
> } > > return -1; > @@ -1235,7 +1244,7 @@ __rmqueue_fallback(struct zone *zone, unsigned int order, int start_migratetype) > --current_order) { > area = &(zone->free_area[current_order]); > fallback_mt = find_suitable_fallback(area, current_order, > - start_migratetype, &can_steal); > + start_migratetype, false, &can_steal); > if (fallback_mt == -1) > continue; > >
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