linux-kernel - Re: [PATCH v3 0/5] xen/blk: persistent grant rework

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Message-ID: <20180817155909.4cwiy6bhhgiala5m@mac>
Date:   Fri, 17 Aug 2018 17:59:09 +0200
From:   Roger Pau Monné <roger.pau@...rix.com>
To:     Juergen Gross <jgross@...e.com>
CC:     <linux-kernel@...r.kernel.org>, <xen-devel@...ts.xenproject.org>,
        <linux-block@...r.kernel.org>, <konrad.wilk@...cle.com>,
        <axboe@...nel.dk>, <boris.ostrovsky@...cle.com>
Subject: Re: [PATCH v3 0/5] xen/blk: persistent grant rework

On Mon, Aug 13, 2018 at 04:01:09PM +0200, Juergen Gross wrote:
> Persistent grants are used in the Xen's blkfront/blkback drivers to
> avoid mapping/unmapping of I/O buffers in the backend for each I/O.
> 
> While this speeds up processing quite a bit there are problems related
> to persistent grants in some configurations: domains with multiple
> block devices making use of persistent grants might suffer from a lack
> of grants if each of the block devices experienced a high I/O load at
> some time. This is due to the number of persistent grants per device
> only to be limited by a rather high maximum value, but never being
> released even in case of longer times without any I/O.
> 
> This series modifies xen-blkback to unmap any domU page mapped via a
> persistent grant after a timeout (default: 60 seconds). The timeout
> is set to its default value again when a persistent grant has been
> used for an I/O.
> 
> xen-blkfront is modified to scan every 10 seconds for persistent grants
> not in use by blkback any more and to remove such grants.
> 
> The last 3 patches are small cleanups of blkfront and blkback drivers.
> 
> V3:
> - patch 1: make timeout parameter static

Konrad if you are OK with this series, could you please send a pull
request to Jens?

Thanks, Roger.