linux-kernel - Re: [PATCH 1/1] mm/page_alloc: add scheduling point to free_unref_page

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Date:   Tue, 8 Mar 2022 16:19:33 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     wangjianxing <wangjianxing@...ngson.cn>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] mm/page_alloc: add scheduling point to
 free_unref_page_list

On Tue, Mar 01, 2022 at 08:38:25PM -0500, wangjianxing wrote:
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 3589febc6..1b96421c8 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -3479,6 +3479,9 @@ void free_unref_page_list(struct list_head *list)
>  		 */
>  		if (++batch_count == SWAP_CLUSTER_MAX) {
>  			local_unlock_irqrestore(&pagesets.lock, flags);
> +
> +			cond_resched();

This isn't safe.  This path can be called from interrupt context
(otherwise we'd be using local_unlock_irq() instead of irqrestore()).