From: Christoph Hellwig <hch@infradead.org>
To: Chris Worley <worleys@gmail.com>
Cc: linuxraid <linux-raid@vger.kernel.org>
Subject: Re: In Direct I/O, no matter how big the read/write, the bio's are all 4KB
Date: Tue, 9 May 2017 13:14:41 -0700 [thread overview]
Message-ID: <20170509201441.GA17309@infradead.org> (raw)
In-Reply-To: <CANWz5fgNgnZ6R9md1TwD16nZzhAzX-t8BaOsN5-x-FfEE3_h3Q@mail.gmail.com>
On Tue, May 09, 2017 at 10:03:24AM -1000, Chris Worley wrote:
> I realize DIO needs to be 4KB aligned,
Actually many file systems do support sector size aligned direct I/O,
which could be 512 byte aligned. But as that's not your point :)
> but why do large I/Os get
> chopped down into 4KB bio's?
They shouldn't. What kernel version is this on?
> Doing a blocktrace of the md device, even though the app is writing at
> 512KB, the MD driver is receiving 4KB bio's.
The direct I/O code is using bio_add_page to build the bios it submits.
It might be interesting to see which of the checks in it triggers
an early return after the first page.
next prev parent reply other threads:[~2017-05-09 20:14 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-09 20:03 In Direct I/O, no matter how big the read/write, the bio's are all 4KB Chris Worley
2017-05-09 20:14 ` Christoph Hellwig [this message]
2017-05-09 21:26 ` Chris Worley
2017-05-10 2:47 ` Ming Lei
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