linux-ext4 - Re: [PATCH 0/1] iomap regression for aio dio 4k writes

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Message-ID: <ZJPJI1t/wdj/L1W2@infradead.org>
Date:   Wed, 21 Jun 2023 21:08:03 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Dave Chinner <david@...morbit.com>,
        Jeremy Bongio <bongiojp@...il.com>, Ted Tso <tytso@....edu>,
        "Darrick J . Wong" <djwong@...nel.org>,
        Allison Henderson <allison.henderson@...cle.com>,
        linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-xfs@...r.kernel.org
Subject: Re: [PATCH 0/1] iomap regression for aio dio 4k writes

On Thu, Jun 22, 2023 at 03:55:52AM +0100, Matthew Wilcox wrote:
> Latency is important for reads, but why is it important for writes?
> There's such a thing as a dependent read, but writes are usually buffered
> and we can wait as long as we like for a write to complete.

That was exactly my reasoning on why I did always defer the write
completions in the initial iomap direct I/O code, and until now no
one has complained.

I could see why people care either about synchronous writes, or polled
io_uring writes, for which we might be able to do the work in the
completion thread context, but for aio writes this feels a bit odd.