Comment 204 for bug 1518457

I am not sure if this is the same bug, but for me kswapd0 goes high-cpu following a page allocation failure in xhci_segment_alloc and I think that this has been occurring since moving to 4.8 on Fedora 24. I don't remember experiencing it before that. Currently on 4.8.15.

I normally boot with 3 or 4 USB 3.0 disks attached and, after the upgrade to 4.8.x noticed that kswapd0 was running at 100%. I went back to 4.7.x and no problem. Searches on this issue frequently referred to USB disks so I unplugged and rebooted.

If I unplug all of my USB 3.0 devices I get a normal boot, even with a USB weather station, keyboard, mouse. Sometimes, one or two USB 3.0 disks is OK too, If I boot with all of the USB 3.0 disks included, I get a kworker page allocation failure and after boot kswapd0 is high-cpu, usually split across 2-4 cores.

If I boot with two USB 3.0 disks and get a normal boot (no page allocation failure and normal kswapd) and then plug in a hub with the rest of the disks (and a USB 3.0 card reader) I get the page allocation failure at that point and kswapd0 goes high-cpu.

I have not looked at them all, but whenever I see kswapd0 high-cpu and I do look, there is the page allocation failure in the log.

The 'perf top' command seems to show different information from time to time but the top contenders are frequently 'shrink_inactive_list', 'inactive_list_is_low', 'find_next_bit', 'shrink_none_memcg', '_raw_spin_lock' to name a few.

Makes me wonder if the xhci allocation failure is the trigger, and fails to clean up on the error exit path, and kswapd0 is just a hapless victim. There is a stack trace (on ubuntu kernel) of the page allocation failure in the dmesg attached to https://bugzilla.redhat.com/show_bug.cgi?id=1395825 on this issue but I have more if it would help.

I have 19GiB free on a 24GiB machine so there should be no memory shortage to prompt swapping or the page allocation failure.

I had also noticed frequently that not all of my USB disks were mounted after boot and that I had to remove and reinsert a disk to use it. IIRC this affected my USB 2.0 disks too and from before the upgrade to 4.8 too.