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Date: Mon, 25 Jan 2021 04:36:31 +0000
From: Matthew Wilcox <willy@infradead.org>
To: Waiman Long <longman@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Alex Shi <alex.shi@linux.alibaba.com>, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm/filemap: Adding missing mem_cgroup_uncharge() to
 __add_to_page_cache_locked()
Message-ID: <20210125043631.GD308988@casper.infradead.org>
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On Sun, Jan 24, 2021 at 11:24:41PM -0500, Waiman Long wrote:
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 5c9d564317a5..aa0e0fb04670 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -835,6 +835,7 @@ noinline int __add_to_page_cache_locked(struct page *page,
>  	XA_STATE(xas, &mapping->i_pages, offset);
>  	int huge = PageHuge(page);
>  	int error;
> +	bool charged = false;

I don't think we need this extra bool.

> @@ -896,6 +898,8 @@ noinline int __add_to_page_cache_locked(struct page *page,
>  
>  	if (xas_error(&xas)) {
>  		error = xas_error(&xas);
> +		if (charged)
> +			mem_cgroup_uncharge(page);
>  		goto error;
>  	}

Better:

-		goto error;
+		goto uncharge;
...
+uncharge:
+	if (!huge)
+		mem_cgroup_uncharge(page);
 error:
...