Date: Tue, 2 Feb 2016 10:20:54 +0100
From: Christoph Hellwig <hch@lst.de>
To: "J. Bruce Fields" <bfields@fieldses.org>
Cc: Kinglong Mee <kinglongmee@gmail.com>,
        "J. Bruce Fields" <bfields@redhat.com>,
        "linux-nfs@vger.kernel.org" <linux-nfs@vger.kernel.org>,
        Trond Myklebust <trond.myklebust@primarydata.com>,
        Christoph Hellwig <hch@lst.de>
Subject: Re: nfsd: supports read buffer from multiples pages
Message-ID: <20160202092054.GA26701@lst.de>
References: <56AE0302.6050101@gmail.com> <20160201183805.GB5499@fieldses.org>
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In-Reply-To: <20160201183805.GB5499@fieldses.org>
Sender: linux-nfs-owner@vger.kernel.org

On Mon, Feb 01, 2016 at 01:38:05PM -0500, J. Bruce Fields wrote:
> This is with the xfs block layout?
> 
> Christoph, do we know anything about average or worst-case sizes for
> that layout update field?

The average is rather small and fits into a single page, the worst
case is basically unlimited:

	(file size / block size) * sizeof(pnfs_block_extent)

by the protocol, and about half that for a non-stupid client as
it would merge consecutive blocks and only trigger something close
to the worst case for a "block allocated, block hole, block allocated, ..."
pattern.