From mboxrd@z Thu Jan 1 00:00:00 1970 From: Lin Feng Subject: Re: [BUG REPORT] [mm-hotplug, aio] aio ring_pages can't be offlined Date: Fri, 30 Nov 2012 11:42:05 +0800 Message-ID: <50B82B0D.8010206@cn.fujitsu.com> References: <1354172098-5691-1-git-send-email-linfeng@cn.fujitsu.com> <20121129153930.477e9709.akpm@linux-foundation.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: viro@zeniv.linux.org.uk, bcrl@kvack.org, kamezawa.hiroyu@jp.fujitsu.com, mhocko@suse.cz, hughd@google.com, cl@linux.com, mgorman@suse.de, minchan@kernel.org, isimatu.yasuaki@jp.fujitsu.com, laijs@cn.fujitsu.com, wency@cn.fujitsu.com, tangchen@cn.fujitsu.com, linux-fsdevel@vger.kernel.org, linux-aio@kvack.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org To: Andrew Morton Return-path: In-Reply-To: <20121129153930.477e9709.akpm@linux-foundation.org> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org hi Andrew, On 11/30/2012 07:39 AM, Andrew Morton wrote: > Tricky. > > I expect the same problem would occur with pages which are under > O_DIRECT I/O. Obviously O_DIRECT pages won't be pinned for such long > periods, but the durations could still be lengthy (seconds). the offline retry timeout duration is 2 minutes, so to O_DIRECT pages seem maybe not a problem for the moment. > > Worse is a futex page, which could easily remain pinned indefinitely. > > 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. thanks for your advice. I want to limit the impact as little as possible, as mentioned above, direct-io seems not a problem, we needn't touch them. Maybe we can just change the use of get_user_pages()(in or around) such as aio ring pages. I will try to find a way to do this. Thanks, linfeng