Re: [PATCH v2] mm/compaction : fix the wrong return value for isolate_migratepages()

[Huang Shijie <b32955@freescale.com>]

hi,
> 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?
there may are many times the cc->migratepages is zero, but the return 
value is ISOLATE_SUCCESS.


> If this is simply a performance issue then minimally COMPACTBLOCKS
yes, My concern is the performance.

the comment of ISOLATE_NONE makes me confused.  :(

If you think we should update the COMPACTBLOCK in this case, my patch is 
wrong.


> still needs to be updated, we still want to see the tracepoint etc. To
ok.
> 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.
>
thanks.
Huang Shijie


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