Re: swap_cluster_info lockdep splat

From: Huang\, Ying
Date: Fri Feb 17 2017 - 02:32:30 EST

Hi, Hugh,

Hugh Dickins <hughd@xxxxxxxxxx> writes:

> On Thu, 16 Feb 2017, Tim Chen wrote:
>> > I do not understand your zest for putting wrappers around every little
>> > thing, making it all harder to follow than it need be. Here's the patch
>> > I've been running with (but you have a leak somewhere, and I don't have
>> > time to search out and fix it: please try sustained swapping and swapoff).
>> >
>> Hugh, trying to duplicate your test case. ÂSo you were doing swapping,
>> then swap off, swap on the swap device and restart swapping?
> Repeated pair of make -j20 kernel builds in 700M RAM, 1.5G swap on SSD,
> 8 cpus; one of the builds in tmpfs, other in ext4 on loop on tmpfs file;
> sizes tuned for plenty of swapping but no OOMing (it's an ancient 2.6.24
> kernel I build, modern one needing a lot more space with a lot less in use).
> How much of that is relevant I don't know: hopefully none of it, it's
> hard to get the tunings right from scratch. To answer your specific
> question: yes, I'm not doing concurrent swapoffs in this test showing
> the leak, just waiting for each of the pair of builds to complete,
> then tearing down the trees, doing swapoff followed by swapon, and
> starting a new pair of builds.
> Sometimes it's the swapoff that fails with ENOMEM, more often it's a
> fork during build that fails with ENOMEM: after 6 or 7 hours of load
> (but timings show it getting slower leading up to that). /proc/meminfo
> did not give me an immediate clue, Slab didn't look surprising but
> I may not have studied close enough.
> I quilt-bisected it as far as the mm-swap series, good before, bad
> after, but didn't manage to narrow it down further because of hitting
> a presumably different issue inside the series, where swapoff ENOMEMed
> much sooner (after 25 mins one time, during first iteration the next).

I found a memory leak in __read_swap_cache_async() introduced by mm-swap
series, and confirmed it via testing. Could you verify whether it fixed
your cases? Thanks a lot for reporting.

Best Regards,
Huang, Ying