Messages in this thread | | | Date | Mon, 07 Apr 2014 16:46:12 +0200 | From | Vlastimil Babka <> | Subject | Re: [PATCH 2/2] mm/compaction: fix to initialize free scanner properly |
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On 04/03/2014 10:57 AM, Heesub Shin wrote: > Free scanner does not works well on systems having zones which do not > span to pageblock-aligned boundary. > > zone->compact_cached_free_pfn is reset when the migration and free > scanner across or compaction restarts. After the reset, if end_pfn of > the zone was not aligned to pageblock_nr_pages, free scanner tries to > isolate free pages from the middle of pageblock to the end, which can > be very small range.
Hm good catch. I think that the same problem can happen (at least theoretically) through zone->compact_cached_free_pfn with CONFIG_HOLES_IN_ZONE enabled. Then compact_cached_free_pfn could be set to a non-aligned-to-pageblock pfn and spoil scans. I'll send a patch that solves it on isolate_freepages() level, which allows further simplification of the function.
Vlastimil
> Signed-off-by: Heesub Shin <heesub.shin@samsung.com> > Cc: Dongjun Shin <d.j.shin@samsung.com> > Cc: Sunghwan Yun <sunghwan.yun@samsung.com> > --- > mm/compaction.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/compaction.c b/mm/compaction.c > index 1ef9144..fefe1da 100644 > --- a/mm/compaction.c > +++ b/mm/compaction.c > @@ -983,7 +983,7 @@ static int compact_zone(struct zone *zone, struct compact_control *cc) > */ > cc->migrate_pfn = zone->compact_cached_migrate_pfn; > cc->free_pfn = zone->compact_cached_free_pfn; > - if (cc->free_pfn < start_pfn || cc->free_pfn > end_pfn) { > + if (cc->free_pfn < start_pfn || cc->free_pfn >= end_pfn) { > cc->free_pfn = end_pfn & ~(pageblock_nr_pages-1); > zone->compact_cached_free_pfn = cc->free_pfn; > } >
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