linux-kernel - Re: [BUG REPORT] [mm-hotplug, aio] aio ring

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Message-ID: <20121130000443.GK18574@lenny.home.zabbo.net>
Date:	Thu, 29 Nov 2012 16:04:43 -0800
From:	Zach Brown <zab@...bo.net>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Lin Feng <linfeng@...fujitsu.com>, viro@...iv.linux.org.uk,
	bcrl@...ck.org, kamezawa.hiroyu@...fujitsu.com, mhocko@...e.cz,
	hughd@...gle.com, cl@...ux.com, mgorman@...e.de,
	minchan@...nel.org, isimatu.yasuaki@...fujitsu.com,
	laijs@...fujitsu.com, wency@...fujitsu.com,
	tangchen@...fujitsu.com, linux-fsdevel@...r.kernel.org,
	linux-aio@...ck.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [BUG REPORT] [mm-hotplug, aio] aio ring_pages can't be offlined

> The best I can think of is to make changes in or around
> get_user_pages(), to steal the pages from userspace and replace them
> with non-movable ones before pinning them.  The performance cost of
> something like this would surely be unacceptable for direct-io, but
> maybe OK for the aio ring and futexes.

In the aio case it seems like it could be taught to populate the mapping
with non-movable pages to begin with.  It's calling get_user_pages() a
few lines after instantiating the mapping itself with do_mmap_pgoff().

- z
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