Messages in this thread | | | Date | Fri, 30 Nov 2012 16:13:16 +0900 | From | Kamezawa Hiroyuki <> | Subject | Re: [BUG REPORT] [mm-hotplug, aio] aio ring_pages can't be offlined |
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(2012/11/30 14:57), Andrew Morton wrote: > On Fri, 30 Nov 2012 11:42:05 +0800 Lin Feng <linfeng@cn.fujitsu.com> 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
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