From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-ID: <50B85C8C.2030702@jp.fujitsu.com> Date: Fri, 30 Nov 2012 16:13:16 +0900 From: Kamezawa Hiroyuki MIME-Version: 1.0 Subject: Re: [BUG REPORT] [mm-hotplug, aio] aio ring_pages can't be offlined References: <1354172098-5691-1-git-send-email-linfeng@cn.fujitsu.com> <20121129153930.477e9709.akpm@linux-foundation.org> <50B82B0D.8010206@cn.fujitsu.com> <20121129215749.acfd872a.akpm@linux-foundation.org> In-Reply-To: <20121129215749.acfd872a.akpm@linux-foundation.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Lin Feng , viro@zeniv.linux.org.uk, bcrl@kvack.org, 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 (2012/11/30 14:57), Andrew Morton wrote: > On Fri, 30 Nov 2012 11:42:05 +0800 Lin Feng wrote: > >> 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. > > What about futexes? > IIUC, futex's key is now a pair of (mm,address) or (inode, pgoff). Then, get_user_page() in futex.c will release the page by put_page(). 'struct page' is just touched by get_futex_key() to obtain page->mapping info. Thanks, -Kame -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org