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Date: Wed, 16 Jun 2010 01:07:57 -0400
From: Christoph Hellwig <hch@infradead.org>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Rik van Riel <riel@redhat.com>, Mel Gorman <mel@csn.ul.ie>,
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       Johannes Weiner <hannes@cmpxchg.org>,
       Christoph Hellwig <hch@infradead.org>,
       Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH 12/12] vmscan: Do not writeback pages in direct reclaim
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On Wed, Jun 16, 2010 at 09:39:58AM +0900, KAMEZAWA Hiroyuki wrote:
> Hmm. But I don't expect copy_from/to_user is called in very deep stack.

Actually it is.  The poll code mentioned earlier in this thread is just
want nasty example.  I'm pretty sure there are tons of others in ioctl
code, as various ioctl implementations have been found to be massive
stack hogs in the past, even worse for out of tree drivers.