Re: [PATCHv2, RFC 05/30] thp, mm: avoid PageUnevictable on active/inactivelru lists

From: Dave Hansen
Date: Thu Mar 21 2013 - 12:14:02 EST

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,
> }
> } else {
> - SetPageUnevictable(page_tail);
> + if (!PageLRU(page) || PageUnevictable(page))
> + SetPageUnevictable(page_tail);
> }

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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