Hi Andrea, On Mon, May 25, 2015 at 04:15:25PM +0200, Andrea Arcangeli wrote: > Hello Christoffer, > > On Sun, May 24, 2015 at 09:34:04PM +0200, Christoffer Dall wrote: > > Hi all, > > > > I noticed a regression on my arm64 APM X-Gene system a couple > > of weeks back. I would occassionally see the system lock up and see RCU > > stalls during the caching phase of kernbench. I then wrote a small > > script that does nothing but cache the files > > (http://paste.ubuntu.com/11324767/) and ran that in a loop. On a known > > bad commit (v4.1-rc2), out of 25 boots, I never saw it get past 21 > > iterations of the loop. I have since tried to run a bisect from v3.19 to > > v4.0 using 100 iterations as my criteria for a good commit. > > > > This resulted in the following first bad commit: > > > > 10359213d05acf804558bda7cc9b8422a828d1cd > > (mm: incorporate read-only pages into transparent huge pages, 2015-02-11) > > > > Indeed, running the workload on v4.1-rc4 still produced the behavior, > > but reverting the above commit gets me through 100 iterations of the > > loop. > > > > I have not tried to reproduce on an x86 system. Turning on a bunch > > of kernel debugging features *seems* to hide the problem. My config for > > the XGene system is defconfig + CONFIG_BRIDGE and > > CONFIG_POWER_RESET_XGENE. > > > > Please let me know if I can help test patches or other things I can > > do to help. I'm afraid that by simply reading the patch I didn't see > > anything obviously wrong with it which would cause this behavior. > > As further confirmation, could you try: > > echo 0 > /sys/kernel/mm/transparent_hugepage/khugepaged/pages_to_scan this returns -EINVAL. But I'm trying now with: echo never > /sys/kernel/mm/transparent_hugepage/enabled > > and verify the problem goes away without having to revert the patch? will let you know, so far so good... > > Accordingly you should reproduce much eaiser this way (setting > $largevalue to 8192 or something, it doesn't matter). > > echo $largevalue > /sys/kernel/mm/transparent_hugepage/khugepaged/pages_to_scan > echo 0 > /sys/kernel/mm/transparent_hugepage/khugepaged/alloc_sleep_millisecs > echo 0 > /sys/kernel/mm/transparent_hugepage/khugepaged/scan_sleep_millisecs > > Then push the system into swap with some memhog -r1000 xG. what is memhog? I couldn't find the utility in Google... I did try with the above settings and just push a bunch of data into ramfs and tmpfs and indeed the sytem died very quickly (on v4.0-rc4). > > The patch just allows readonly anon pages to be collapsed along with > read-write ones, the vma permissions allows it, so they have to be > swapcache pages, this is why swap shall be required. > > Perhaps there's some arch detail that needs fixing but it'll be easier > to track it down once you have a way to reproduce fast. > Yes, would be great to be able to reproduce quickly. Thanks, -Christoffer -- 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>