From: Christoph Hellwig <hch@infradead.org>
To: Ming Lei <ming.lei@canonical.com>
Cc: Christoph Hellwig <hch@infradead.org>,
Jens Axboe <axboe@kernel.dk>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Dave Kleikamp <dave.kleikamp@oracle.com>,
Zach Brown <zab@zabbo.net>,
Maxim Patlasov <mpatlasov@parallels.com>,
Andrew Morton <akpm@linux-foundation.org>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Tejun Heo <tj@kernel.org>, Dave Chinner <david@fromorbit.com>
Subject: Re: [PATCH v9 6/6] block: loop: support DIO & AIO
Date: Sun, 9 Aug 2015 06:44:04 -0700 [thread overview]
Message-ID: <20150809134404.GA7190@infradead.org> (raw)
In-Reply-To: <CACVXFVO9Wpa+9QWCzMOVQOramd1KsfvtC=vcf-EsCQum-9Omuw@mail.gmail.com>
On Sun, Aug 09, 2015 at 09:04:32AM -0400, Ming Lei wrote:
> Now the logical block size of loop is 512byte, but the sector size of
> backing device may be 4K, so we can't do 512 byte algined direct
> I/O to the filesystem in this situation.
>
> With runtime switch to buffered I/O we can fix this problem, but
> most of times it won't fall in this case.
The right way to handle this case is to not allow direct I/O at all,
you'll be constantly switching between direct and buffered I/O
otherwise, which is a bad idea.
> For non-512 byte sector size of backing device, it is needed as
> I described above.
If the backing device sector size is smaller than that of the loop
device you should not allow direct I/O as you will be switching forth
and back ue to the IO patterns all the time.
next prev parent reply other threads:[~2015-08-09 13:44 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-08-06 8:42 [PATCH v9 0/6] block: loop: improve loop with AIO Ming Lei
2015-08-06 8:42 ` [PATCH v9 1/6] fs: direct-io: don't dirtying pages for ITER_BVEC/ITER_KVEC direct read Ming Lei
2015-08-06 8:42 ` [PATCH v9 2/6] block: loop: set QUEUE_FLAG_NOMERGES for request queue of loop Ming Lei
2015-08-06 8:42 ` [PATCH v9 3/6] block: loop: use kthread_work Ming Lei
2015-08-06 8:42 ` [PATCH v9 4/6] block: loop: prepare for supporing direct IO Ming Lei
2015-08-06 8:42 ` [PATCH v9 5/6] block: loop: introduce ioctl command of LOOP_SET_DIRECT_IO Ming Lei
2015-08-06 8:42 ` [PATCH v9 6/6] block: loop: support DIO & AIO Ming Lei
2015-08-07 7:43 ` Christoph Hellwig
2015-08-07 8:25 ` Ming Lei
2015-08-09 6:44 ` Christoph Hellwig
2015-08-09 13:04 ` Ming Lei
2015-08-09 13:44 ` Christoph Hellwig [this message]
2015-08-09 14:27 ` Ming Lei
2015-08-09 23:41 ` Dave Chinner
2015-08-10 2:50 ` Ming Lei
2015-08-10 8:08 ` Christoph Hellwig
2015-08-10 14:33 ` Ming Lei
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