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Date:   Thu, 12 Sep 2019 08:57:29 +0800
From:   Ming Lei <ming.lei@redhat.com>
To:     Christoph Hellwig <hch@lst.de>
Cc:     Thierry Reding <thierry.reding@gmail.com>,
        Jens Axboe <axboe@kernel.dk>,
        Ulf Hansson <ulf.hansson@linaro.org>,
        Adrian Hunter <adrian.hunter@intel.com>,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>,
        Simon Horman <horms+renesas@verge.net.au>,
        Jon Hunter <jonathanh@nvidia.com>, linux-block@vger.kernel.org,
        linux-mmc@vger.kernel.org, linux-tegra@vger.kernel.org
Subject: Re: [PATCH 1/3] block: Respect the device's maximum segment size
Message-ID: <20190912005728.GA2731@ming.t460p>
References: <20190909125658.30559-1-thierry.reding@gmail.com>
 <20190909125658.30559-2-thierry.reding@gmail.com>
 <20190909161331.GA19650@lst.de>
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On Mon, Sep 09, 2019 at 06:13:31PM +0200, Christoph Hellwig wrote:
> On Mon, Sep 09, 2019 at 02:56:56PM +0200, Thierry Reding wrote:
> > From: Thierry Reding <treding@nvidia.com>
> > 
> > When enabling the DMA map merging capability for a queue, ensure that
> > the maximum segment size does not exceed the device's limit.
> 
> We can't do that unfortunately.  If we use the virt_boundary setting
> we do aggressive merges that there is no accounting for.  So we can't
> limit the segment size.

Could you explain a bit why we can't do that?

The segment size limit is basically removed since the following commit
200a9aff7b02 ("block: remove the segment size check in bio_will_gap").

Before that commit, the max segment size limit worked.


Thanks,
Ming