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Date:   Mon, 14 Feb 2022 23:19:22 -0800
From:   Christoph Hellwig <hch@infradead.org>
To:     "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc:     linux-fsdevel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH 04/10] mm/truncate: Replace page_mapped() call in
 invalidate_inode_page()
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On Mon, Feb 14, 2022 at 08:00:11PM +0000, Matthew Wilcox (Oracle) wrote:
> folio_mapped() is expensive because it has to check each page's mapcount
> field.  A cheaper check is whether there are any extra references to
> the page, other than the one we own and the ones held by the page cache.
> The call to remove_mapping() will fail in any case if it cannot freeze
> the refcount, but failing here avoids cycling the i_pages spinlock.

I wonder if something like this should also be in a comment near
the check in the code.