On 11/30/2012 01:57 PM, Andrew Morton wrote: > On Fri, 30 Nov 2012 11:42:05 +0800 Lin Feng <linfeng@xxxxxxxxxxxxxx> 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? hi Andrew, Yes, better to find an approach to solve them all. But I'm worried about that if we just confine get_user_pages() to use none-movable pages, it will drain the none-movable pages soon. Because there are many places using get_user_pages() such as some drivers. IMHO in most cases get_user_pages() callers should release the pages soon, so pages allocated from movable zone should be OK. But I'm not sure if we get such rule upon get_user_pages(). And in other cases we specify get_user_pages() to allocate pages from none-movable zone. So could we add a zone-alloc flags when we call get_user_pages()? Thanks, linfeng > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>