Re: [External] Re: [PATCH] files: Use rcu lock to get the file structures for better performance

On Fri, May 22, 2020 at 12:06:46AM +0800, Muchun Song wrote:

On Thu, May 21, 2020 at 11:21 PM Matthew Wilcox [off-list ref] wrote:

quoted

On Thu, May 21, 2020 at 08:38:35PM +0800, Muchun Song wrote:

quoted

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?

I have read the doc which is in the Documentation/filesystems/files.txt.
If my understanding is correct, I think it is safe to use rcu lock.

Did you test this and prove that it is safe and "faster"?  If so, you
always have to show that in your changelog.  Please fix it up and
resend.

thanks,

greg k-h