linux-kernel - Re: [PATCH 6/6] mm: workingset: restore refault tracking for single-page files

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Date:   Tue, 8 Nov 2016 11:31:19 +0100
From:   Jan Kara <jack@...e.cz>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jan Kara <jack@...e.cz>,
        "Kirill A. Shutemov" <kirill@...temov.name>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, kernel-team@...com
Subject: Re: [PATCH 6/6] mm: workingset: restore refault tracking for
 single-page files

On Mon 07-11-16 14:07:41, Johannes Weiner wrote:
> Shadow entries in the page cache used to be accounted behind the radix
> tree implementation's back in the upper bits of node->count, and the
> radix tree code extending a single-entry tree with a shadow entry in
> root->rnode would corrupt that counter. As a result, we could not put
> shadow entries at index 0 if the tree didn't have any other entries,
> and that means no refault detection for any single-page file.
> 
> Now that the shadow entries are tracked natively in the radix tree's
> exceptional counter, this is no longer necessary. Extending and
> shrinking the tree from and to single entries in root->rnode now does
> the right thing when the entry is exceptional, remove that limitation.
> 
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>

The patch looks good to me. You can add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  mm/filemap.c | 13 +++----------
>  1 file changed, 3 insertions(+), 10 deletions(-)
> 
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 438f0b54f8fd..55a3b136a527 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -178,19 +178,12 @@ static void page_cache_tree_delete(struct address_space *mapping,
>  
>  		radix_tree_clear_tags(&mapping->page_tree, node, slot);
>  
> -		if (!node) {
> -			VM_BUG_ON_PAGE(nr != 1, page);
> -			/*
> -			 * We need a node to properly account shadow
> -			 * entries. Don't plant any without. XXX
> -			 */
> -			shadow = NULL;
> -		}
> -
>  		__radix_tree_replace(&mapping->page_tree, node, slot, shadow);
>  
> -		if (!node)
> +		if (!node) {
> +			VM_BUG_ON_PAGE(nr != 1, page);
>  			break;
> +		}
>  
>  		if (!shadow &&
>  		    __radix_tree_delete_node(&mapping->page_tree, node))
> -- 
> 2.10.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR