On 26 May 2015 at 15:35, Christoffer Dall <christoffer.dall@xxxxxxxxxx> wrote: > Hi Steve, > > On Tue, May 26, 2015 at 03:24:20PM +0100, Steve Capper wrote: >> >> 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. >> > > >> I'm trying to reproduce this on hardware here; but have been unable to >> thus far with 4.1-rc2 on a Xgene and Seattle systems. > > Really? That's concerning. I think Andre mentioned he could > reproduce... > > How many iterations have you run the caching loop for? > > Are you using defconfig? I noticed that turning on debugging features > was hiding the problem. > >> Also, I tried the memhog + pages_to_scan suggestion from Andrea. > > Any chance you could send me the memhog tool? > >> >> Maybe a silly question, where is your root filesystem located? Is >> there anything network mounted? >> > It's a regular ext4 on the local SATA disk. Ubuntu Trusty. > > Thanks, > -Christoffer Sending an email to lakml appears to have been enough to make it hang on the Xgene :-). The system is completely frozen, not even the serial port works. On Seattle, I've hit 100 iterations multiple times without any problems. Investigating... Cheers, -- Steve -- 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>