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@xxxxxxxxxxx>
The patch looks good to me. You can add:
Reviewed-by: Jan Kara <jack@xxxxxxx>
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@xxxxxxxx>
SUSE Labs, CR
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