linux-kernel - Re: [PATCHv2, RFC 05/30] thp, mm: avoid PageUnevictable on active/inactive lru lists

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Message-ID: <514B320C.4030507@sr71.net>
Date:	Thu, 21 Mar 2013 09:15:08 -0700
From:	Dave Hansen <dave@...1.net>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
CC:	Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Hugh Dickins <hughd@...gle.com>,
	Wu Fengguang <fengguang.wu@...el.com>, Jan Kara <jack@...e.cz>,
	Mel Gorman <mgorman@...e.de>, linux-mm@...ck.org,
	Andi Kleen <ak@...ux.intel.com>,
	Matthew Wilcox <matthew.r.wilcox@...el.com>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Hillf Danton <dhillf@...il.com>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2, RFC 05/30] thp, mm: avoid PageUnevictable on active/inactive
 lru lists

On 03/14/2013 10:50 AM, Kirill A. Shutemov wrote:
> active/inactive lru lists can contain unevicable pages (i.e. ramfs pages
> that have been placed on the LRU lists when first allocated), but these
> pages must not have PageUnevictable set - otherwise shrink_active_list
> goes crazy:
...
> For lru_add_page_tail(), it means we should not set PageUnevictable()
> for tail pages unless we're sure that it will go to LRU_UNEVICTABLE.
> The tail page will go LRU_UNEVICTABLE if head page is not on LRU or if
> it's marked PageUnevictable() too.

This is only an issue once you're using lru_add_page_tail() for
non-anonymous pages, right?

> diff --git a/mm/swap.c b/mm/swap.c
> index 92a9be5..31584d0 100644
> --- a/mm/swap.c
> +++ b/mm/swap.c
> @@ -762,7 +762,8 @@ void lru_add_page_tail(struct page *page, struct page *page_tail,
>  			lru = LRU_INACTIVE_ANON;
>  		}
>  	} else {
> -		SetPageUnevictable(page_tail);
> +		if (!PageLRU(page) || PageUnevictable(page))
> +			SetPageUnevictable(page_tail);
>  		lru = LRU_UNEVICTABLE;
>  	}

You were saying above that ramfs pages can get on the normal
active/inactive lists.  But, this will end up getting them on the
unevictable list, right?  So, we have normal ramfs pages on the
active/inactive lists, but ramfs pages after a huge-page-split on the
unevictable list.  That seems a bit inconsistent.
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