linux-kernel - Re: [PATCH 1/3] block: loop: use kmap(page) instead of page

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Message-ID: <20150324102905.GA7002@lst.de>
Date:	Tue, 24 Mar 2015 11:29:05 +0100
From:	Christoph Hellwig <hch@....de>
To:	Ming Lei <ming.lei@...onical.com>
Cc:	Jens Axboe <axboe@...com>, linux-kernel@...r.kernel.org,
	Christoph Hellwig <hch@....de>,
	Al Viro <viro@...iv.linux.org.uk>,
	Maxim Patlasov <mpatlasov@...allels.com>
Subject: Re: [PATCH 1/3] block: loop: use kmap(page) instead of
	page_address(page)

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.
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