On Sat, Dec 31, 2011 at 05:09:45PM +0800, Huang Shijie wrote:
> When we do not get any migrate page, we should return ISOLATE_NONE.
>
Why?
Returning ISOLATE_SUCCESS means that we fall through. This means busy
work in migrate_pages(), updating list accounting and the list. It's
wasteful but is it functionally incorrect? What problem did you observe?
If this is simply a performance issue then minimally COMPACTBLOCKS
still needs to be updated, we still want to see the tracepoint etc. To
preserve that, I would suggest as an alternative to leave it returning
ISOLATE_SUCCESS but move
err = migrate_pages(&cc->migratepages, compaction_alloc,
(unsigned long)cc, false,
cc->sync ? MIGRATE_SYNC_LIGHT : MIGRATE_ASYNC);
update_nr_listpages(cc);
inside a if (nr_migrate) check to avoid some overhead.
--
Mel Gorman
SUSE Labs
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