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

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Message-ID: <20150324110951.GA7979@lst.de>
Date:	Tue, 24 Mar 2015 12:09:51 +0100
From:	Christoph Hellwig <hch@....de>
To:	Ming Lei <ming.lei@...onical.com>
Cc:	Christoph Hellwig <hch@....de>, Jens Axboe <axboe@...com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	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 Tue, Mar 24, 2015 at 06:49:00PM +0800, Ming Lei wrote:
> On 32bit system, this still may cause pressure on page allocation, since
> requests are handled concurrently now after using workqueue.

kmap slots are from a much smaller resource pool than non-highmem
allocations, so if a page needs to stay kmaped from allocation time until
freeing it it should just be allocated as a kernel mapped page.
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