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Date: Tue, 24 Mar 2015 11:29:05 +0100
From: Christoph Hellwig <hch@lst.de>
To: Ming Lei <ming.lei@canonical.com>
Cc: Jens Axboe <axboe@fb.com>, linux-kernel@vger.kernel.org,
        Christoph Hellwig <hch@lst.de>, Al Viro <viro@zeniv.linux.org.uk>,
        Maxim Patlasov <mpatlasov@parallels.com>
Subject: Re: [PATCH 1/3] block: loop: use kmap(page) instead of
	page_address(page)
Message-ID: <20150324102905.GA7002@lst.de>
References: <1427012095-4095-1-git-send-email-ming.lei@canonical.com> <1427012095-4095-2-git-send-email-ming.lei@canonical.com>
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On Sun, Mar 22, 2015 at 04:14:52PM +0800, Ming Lei wrote:
> The raw page allocated in lo_send() can be a highmem page,
> so kmap(page) should be used for read/write on the page.
> 
> Also the patch removes kmap()/kunmap() in lo_send() because
> it isn't needed at all.

The description seems odd, what it seems to do is to shift the
kmap from lo_send into do_lo_send_write.  This does not seem
very useful as it now means a kmap per segment instead of just
a single one per I/O.  What would make more sense is to just
not allocate a highmem page.