linux-kernel - Re: [PATCH v2] vmscan: fix increasing nr_isolated incurred by putback unevictable pages

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Message-Id: <20150804150937.ee3b62257e77911a2f41a48e@linux-foundation.org>
Date:	Tue, 4 Aug 2015 15:09:37 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Jaewon Kim <jaewon31.kim@...sung.com>
Cc:	mgorman@...e.de, minchan@...nel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, jaewon31.kim@...il.com
Subject: Re: [PATCH v2] vmscan: fix increasing nr_isolated incurred by
 putback unevictable pages

On Tue, 04 Aug 2015 19:40:08 +0900 Jaewon Kim <jaewon31.kim@...sung.com> wrote:

> reclaim_clean_pages_from_list() assumes that shrink_page_list() returns
> number of pages removed from the candidate list. But shrink_page_list()
> puts back mlocked pages without passing it to caller and without
> counting as nr_reclaimed. This incurrs increasing nr_isolated.
> To fix this, this patch changes shrink_page_list() to pass unevictable
> pages back to caller. Caller will take care those pages.
> 
> ..
>
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1157,7 +1157,7 @@ cull_mlocked:
>  		if (PageSwapCache(page))
>  			try_to_free_swap(page);
>  		unlock_page(page);
> -		putback_lru_page(page);
> +		list_add(&page->lru, &ret_pages);
>  		continue;
>  
>  activate_locked:

Is this going to cause a whole bunch of mlocked pages to be migrated
whereas in current kernels they stay where they are?

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