linux-kernel - Re: [PATCH V2 0/2] Auto stop async-write on block device when device removed.

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Message-ID: <x49siwsewhx.fsf@segfault.boston.devel.redhat.com>
Date:	Wed, 25 Sep 2013 11:44:58 -0400
From:	Jeff Moyer <jmoyer@...hat.com>
To:	majianpeng <majianpeng@...il.com>
Cc:	axboe <axboe@...nel.dk>, viro <viro@...iv.linux.org.uk>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH V2 0/2] Auto stop async-write on block device when device removed.

majianpeng <majianpeng@...il.com> writes:

>>The bigger question is whether we want to change this long-standing
>>behaviour of how our write-back cache works.  I don't know that it's
>>really worth it, honestly.  If you want to ensure data is on disk, you
>>open the file O_SYNC or you issue an fsync, and those calls will return
>>an error for a removed block device.  So, I guess I'll ask the same
>>question again: why are you looking at this?  Is there some application
>>you care about that does buffered I/O to the block device and never does
>>an fsync?
>>
> Yes, for my company, we used our filesystem in userspace on block-device.
> For the performance, we used buffer-wrtite not sync-write.
> For my workload, we allow user to remove disk whether disk working or not.
> Now, we check the state of disk from /proc/partitions at the same interval.
>
> This patchset don't change write-back cache works.It only let vfs know
> the state of lower-device.  I think it make a sense.

I'm still curious to know how you maintain a consistent file system
without the use of fsync, but that's an unrelated issue.

I looked at the rescan partition code path more closely, and it will
only really trigger if the partitions themselves aren't open.  So, I
don't think there is a problem in your approach.

I'll ack patch 1.  I still think patch 2 is not neessary.  Please
correct me if I'm wrong.

Cheers,
Jeff
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