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Date:   Thu, 22 Sep 2022 07:39:17 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Bart Van Assche <bvanassche@acm.org>
Cc:     Jens Axboe <axboe@kernel.dk>, Christoph Hellwig <hch@lst.de>,
        Ming Lei <ming.lei@redhat.com>,
        Jaegeuk Kim <jaegeuk@kernel.org>,
        "linux-block@vger.kernel.org" <linux-block@vger.kernel.org>
Subject: Re: Supporting segment sizes smaller than the page size
Message-ID: <20220922053917.GA27293@lst.de>
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On Wed, Sep 21, 2022 at 04:28:32PM -0700, Bart Van Assche wrote:
> I have been asked to add support for DMA segment sizes that are smaller 
> than the page size to support a UFS controller with a maximum DMA segment 
> size of 4 KiB and a page size > 4 KiB (my understanding of the JEDEC UFS 
> host controller specification is that UFS host controllers should support a 
> maximum DMA segment size of 256 KiB). Does anyone want to comment on this 
> before I start working on a patch series?

Don't do it.  This gets us into all kinds of corner cases, and even
worse now requires to do the expensive segment walk for every I/O while
right now we have a nice little fast path.