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Date: Tue, 24 Mar 2015 12:09:51 +0100
From: Christoph Hellwig <hch@lst.de>
To: Ming Lei <ming.lei@canonical.com>
Cc: Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@fb.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        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: <20150324110951.GA7979@lst.de>
References: <1427012095-4095-1-git-send-email-ming.lei@canonical.com> <1427012095-4095-2-git-send-email-ming.lei@canonical.com> <20150324102905.GA7002@lst.de> <CACVXFVMcC4G5s0-JT1Z8APup18MKwGAkN7qyubxDW-ByTVxtRA@mail.gmail.com>
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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.