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Date:   Tue, 15 Dec 2020 20:03:57 +0800
From:   Ming Lei <>
To:     Pavel Begunkov <>
Cc:, Jens Axboe <>,
        Christoph Hellwig <>,
        Matthew Wilcox <>,
        Johannes Weiner <>,
        Alexander Viro <>,
        "Darrick J . Wong" <>,
        "Martin K . Petersen" <>,
        Jonathan Corbet <>,,,,,,,
Subject: Re: [PATCH v1 0/6] no-copy bvec

On Tue, Dec 15, 2020 at 11:14:20AM +0000, Pavel Begunkov wrote:
> On 15/12/2020 01:41, Ming Lei wrote:
> > On Tue, Dec 15, 2020 at 12:20:19AM +0000, Pavel Begunkov wrote:
> >> Instead of creating a full copy of iter->bvec into bio in direct I/O,
> >> the patchset makes use of the one provided. It changes semantics and
> >> obliges users of asynchronous kiocb to track bvec lifetime, and [1/6]
> >> converts the only place that doesn't.
> > 
> > Just think of one corner case: iov_iter(BVEC) may pass bvec table with zero
> > length bvec, which may not be supported by block layer or driver, so
> > this patchset has to address this case first.
> The easiest for me would be to fallback to copy if there are zero bvecs,
> e.g. finding such during iov_iter_alignment(), but do we know from where
> zero bvecs can came? As it's internals we may want to forbid them if
> there is not too much hassle.

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