linux-kernel - Re: [PATCH 08/11] xen-blkfront: remove bio splitting.

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Message-ID: <20170421114622.ymoprc7a4h3g6xqi@dhcp-3-128.uk.xensource.com>
Date:   Fri, 21 Apr 2017 12:46:22 +0100
From:   Roger Pau Monne <roger.pau@...rix.com>
To:     Christoph Hellwig <hch@...radead.org>
CC:     NeilBrown <neilb@...e.com>, Jens Axboe <axboe@...nel.dk>,
        <linux-block@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        <xen-devel@...ts.xenproject.org>
Subject: Re: [PATCH 08/11] xen-blkfront: remove bio splitting.

On Fri, Apr 21, 2017 at 04:36:20AM -0700, Christoph Hellwig wrote:
> Btw, I really don't understand why this code even looks at bios over
> just requeueing the request.  Can someone explain that bit to me?

This was done because Linux could migrate from a host supporting indirect
descriptors to a host not supporting them, and so the maximum number of
segments per request could change, and the requests already on the queue might
need to be split.

Roger.