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Date:   Sun, 22 May 2022 09:45:09 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Jens Axboe <axboe@kernel.dk>
Cc:     Al Viro <viro@zeniv.linux.org.uk>, Christoph Hellwig <hch@lst.de>,
        Matthew Wilcox <willy@infradead.org>,
        linux-fsdevel@vger.kernel.org
Subject: Re: [RFC] what to do with IOCB_DSYNC?
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On Sat, May 21, 2022 at 04:14:07PM -0600, Jens Axboe wrote:
> Then we're almost on par, and it looks like we just need to special case
> iov_iter_advance() for the nr_segs == 1 as well to be on par. This is on
> top of your patch as well, fwiw.
> 
> It might make sense to special case the single segment cases, for both
> setup, iteration, and advancing. With that, I think we'll be where we
> want to be, and there will be no discernable difference between the iter
> paths and the old style paths.

A while ago willy posted patches to support a new ITER type for direct
userspace pointer without iov.  It might be worth looking through the
archives and test that.