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From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: Mel Gorman <mel@csn.ul.ie>
Subject: Re: [PATCH 02/11] mm,migration: Do not try to migrate unmapped anonymous pages
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       KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
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very small nit

> There were minor changes in how the rcu_read_lock is taken and released
> based on other comments. With your suggestion, the block now looks like;
> 
>         if (PageAnon(page)) {
>                 rcu_read_lock();
>                 rcu_locked = 1;
> 
>                 /*
>                  * If the page has no mappings any more, just bail. An
>                  * unmapped anon page is likely to be freed soon but
>                  * worse,
>                  * it's possible its anon_vma disappeared between when
>                  * the page was isolated and when we reached here while
>                  * the RCU lock was not held
>                  */
>                 if (!page_mapcount(page) && !PageSwapCache(page))

                        page_mapped?

>                         goto rcu_unlock;
> 
>                 anon_vma = page_anon_vma(page);
>                 atomic_inc(&anon_vma->external_refcount);
>         }