linux-kernel - Re: [PATCH 3/4] mm: workingset: add vmstat counter for shadow nodes

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Date:   Tue, 9 Oct 2018 15:08:45 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     Rik van Riel <riel@...hat.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, kernel-team@...com
Subject: Re: [PATCH 3/4] mm: workingset: add vmstat counter for shadow nodes

On Tue,  9 Oct 2018 14:47:32 -0400 Johannes Weiner <hannes@...xchg.org> wrote:

> --- a/mm/workingset.c
> +++ b/mm/workingset.c
> @@ -378,11 +378,17 @@ void workingset_update_node(struct xa_node *node)
>  	 * as node->private_list is protected by the i_pages lock.
>  	 */
>  	if (node->count && node->count == node->nr_values) {
> -		if (list_empty(&node->private_list))
> +		if (list_empty(&node->private_list)) {
>  			list_lru_add(&shadow_nodes, &node->private_list);
> +			__inc_lruvec_page_state(virt_to_page(node),
> +						WORKINGSET_NODES);
> +		}
>  	} else {
> -		if (!list_empty(&node->private_list))
> +		if (!list_empty(&node->private_list)) {
>  			list_lru_del(&shadow_nodes, &node->private_list);
> +			__dec_lruvec_page_state(virt_to_page(node),
> +						WORKINGSET_NODES);
> +		}
>  	}
>  }

A bit worried that we're depending on the caller's caller to have
disabled interrupts to avoid subtle and rare errors.

Can we do this?

--- a/mm/workingset.c~mm-workingset-add-vmstat-counter-for-shadow-nodes-fix
+++ a/mm/workingset.c
@@ -377,6 +377,8 @@ void workingset_update_node(struct radix
 	 * already where they should be. The list_empty() test is safe
 	 * as node->private_list is protected by the i_pages lock.
 	 */
+	WARN_ON_ONCE(!irqs_disabled());	/* For __inc_lruvec_page_state */
+
 	if (node->count && node->count == node->exceptional) {
 		if (list_empty(&node->private_list)) {
 			list_lru_add(&shadow_nodes, &node->private_list);
_