(2012/11/30 14:57), 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?
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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