Re: [PATCH 2/9] vfs: export do_splice_direct() to modules

From: David Howells
Date: Tue Mar 19 2013 - 07:05:22 EST

Miklos Szeredi <miklos@xxxxxxxxxx> wrote:

> > BTW, I wonder what's the right locking for that sucker; overlayfs is
> > probably too heavy - we are talking about copying a file from one fs to
> > another, which can obviously take quite a while, so holding ->i_mutex on
> > _parent_ all along is asking for very serious contention.
> Copy up is a once-in-a-lifetime event for an object. Optimizing it is
> way down in the list of things to do. I'd drop splice in a jiffy if
> it's in the way.

Yes, but it could block the parent directory for a long time. I suspect it's
fine if you can RCU walk through the parent, but if you have to grab a lock on

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