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Date:   Fri, 10 Sep 2021 02:57:54 +0000
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Jens Axboe <axboe@kernel.dk>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Pavel Begunkov <asml.silence@gmail.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>
Subject: Re: [git pull] iov_iter fixes
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On Thu, Sep 09, 2021 at 03:19:56PM -0600, Jens Axboe wrote:

> Not sure how we'd do that, outside of stupid tricks like copy the
> iov_iter before we pass it down. But that's obviously not going to be
> very efficient. Hence we're left with having some way to reset/reexpand,
> even in the presence of someone having done truncate on it.

"Obviously" why, exactly?  It's not that large a structure; it's not
the optimal variant, but I'd like to see profiling data before assuming
that it'll cause noticable slowdowns.