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Date:   Mon, 17 Jan 2022 23:25:14 -0800
From:   Christoph Hellwig <hch@infradead.org>
To:     Matthew Wilcox <willy@infradead.org>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
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Subject: Re: Out of order read() completion and buffer filling beyond
 returned amount
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On Mon, Jan 17, 2022 at 01:30:05PM +0000, Matthew Wilcox wrote:
> I think for DIO, you're sacrificing the entire buffer with any filesystem.
> If the underlying file is split across multiple drives, or is even
> just fragmented on a single drive, we'll submit multiple BIOs which
> will complete independently (even for SCSI which writes sequentially;
> never mind NVMe which can DMA blocks asynchronously).  It might be
> more apparent in a networking situation where errors are more common,
> but it's always been a possibility since Linux introduced DIO.

Yes.  Probably because of that we also never allow short reads or writes
due to I/O errrors but always fail the whole I/O.