linux-kernel - Re: [PATCH] NFSv4.1: PNFS_BLOCK_NONE_DATA should be handle properly in bl_add_merge

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Message-ID: <20140120135231.GA17536@infradead.org>
Date:	Mon, 20 Jan 2014 05:52:31 -0800
From:	Christoph Hellwig <hch@...radead.org>
To:	shaobingqing <shaobingqing@...tor.com.cn>
Cc:	trond.myklebust@...marydata.com, linux-nfs@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] NFSv4.1: PNFS_BLOCK_NONE_DATA should be handle properly
 in bl_add_merge_extent?

On Mon, Jan 20, 2014 at 06:07:28PM +0800, shaobingqing wrote:
> In the current code, extents would not delete from the bl_extents list when 
> lseg is removed from layout. Now one extent's lseg is deleted and its type 
> is PNFS_BLOCK_NONE_DATA, while a layoutget request get a extent with the same
> range and its type is PNFS_BLOCK_NONE_DATA. In this situation the function
> bl_add_merge_extent will return -EIO. Furthermore, the READ op which request
> the layout will be execute in band. This perhaps not only degrade performance,
> but also result in data unconsistency. 

I think the right fix is to remove the extent when the lseg is removed.
I can't see how the current pnfs block client could work in the case
where a file is first truncated and then later written into again.

This should be easily reproducable using fsx, btw.

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