Re: [PATCH 2/6] mm: workingset: turn shadow node shrinker bugs into warnings

[Jan Kara <jack@suse.cz>]

On Mon 07-11-16 14:07:37, Johannes Weiner wrote:
> When the shadow page shrinker tries to reclaim a radix tree node but
> finds it in an unexpected state - it should contain no pages, and
> non-zero shadow entries - there is no need to kill the executing task
> or even the entire system. Warn about the invalid state, then leave
> that tree node be. Simply don't put it back on the shadow LRU for
> future reclaim and move on.
> 
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>

The patch looks good to me. You can add:

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

								Honza

> ---
>  mm/workingset.c | 20 ++++++++++++--------
>  1 file changed, 12 insertions(+), 8 deletions(-)
> 
> diff --git a/mm/workingset.c b/mm/workingset.c
> index 617475f529f4..3cfc61d84a52 100644
> --- a/mm/workingset.c
> +++ b/mm/workingset.c
> @@ -418,23 +418,27 @@ static enum lru_status shadow_lru_isolate(struct list_head *item,
>  	 * no pages, so we expect to be able to remove them all and
>  	 * delete and free the empty node afterwards.
>  	 */
> -	BUG_ON(!workingset_node_shadows(node));
> -	BUG_ON(workingset_node_pages(node));
> -
> +	if (WARN_ON_ONCE(!workingset_node_shadows(node)))
> +		goto out_invalid;
> +	if (WARN_ON_ONCE(workingset_node_pages(node)))
> +		goto out_invalid;
>  	for (i = 0; i < RADIX_TREE_MAP_SIZE; i++) {
>  		if (node->slots[i]) {
> -			BUG_ON(!radix_tree_exceptional_entry(node->slots[i]));
> +			if (WARN_ON_ONCE(!radix_tree_exceptional_entry(node->slots[i])))
> +				goto out_invalid;
> +			if (WARN_ON_ONCE(!mapping->nrexceptional))
> +				goto out_invalid;
>  			node->slots[i] = NULL;
>  			workingset_node_shadows_dec(node);
> -			BUG_ON(!mapping->nrexceptional);
>  			mapping->nrexceptional--;
>  		}
>  	}
> -	BUG_ON(workingset_node_shadows(node));
> +	if (WARN_ON_ONCE(workingset_node_shadows(node)))
> +		goto out_invalid;
>  	inc_node_state(page_pgdat(virt_to_page(node)), WORKINGSET_NODERECLAIM);
> -	if (!__radix_tree_delete_node(&mapping->page_tree, node))
> -		BUG();
> +	__radix_tree_delete_node(&mapping->page_tree, node);
>  
> +out_invalid:
>  	spin_unlock(&mapping->tree_lock);
>  	ret = LRU_REMOVED_RETRY;
>  out:
> -- 
> 2.10.1
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

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