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Date:   Thu, 21 May 2020 08:21:17 -0700
From:   Matthew Wilcox <willy@infradead.org>
To:     Muchun Song <songmuchun@bytedance.com>
Cc:     adobriyan@gmail.com, ast@kernel.org, daniel@iogearbox.net,
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Subject: Re: [PATCH] files: Use rcu lock to get the file structures for
 better performance
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On Thu, May 21, 2020 at 08:38:35PM +0800, Muchun Song wrote:
> There is another safe way to get the file structure without
> holding the files->file_lock. That is rcu lock, and this way
> has better performance. So use the rcu lock instead of the
> files->file_lock.

What makes you think this is safe?  Are you actually seeing contention
on this spinlock?