* Dr. David Alan Gilbert (dgilbert@xxxxxxxxxx) wrote: > * Li, Liang Z (liang.z.li@xxxxxxxxx) wrote: > > > > > > > > > Interesting; it's failing reliably for me - but only with a > > > > > > > > > reasonably freshly booted machine (so that the pages get THPd). > > > > > > > > > > > > > > > > The same here. Freshly booted machine with 64GiB ram. I've > > > > > > > > checked > > > > > > > > /proc/vmstat: huge pages were allocated > > > > > > > > > > > > > > Thanks for testing. > > > > > > > > > > > > > > Damn; this is confusing now. I've got a RHEL7 box with > > > > > > > 4.6.0-rc3 on where it works, and a fedora24 VM where it fails > > > > > > > (the f24 VM is where I did the bisect so it works fine with the > > > > > > > older kernel on the f24 > > > > > userspace in that VM). > > > > > > > > > > > > > > So lets see: > > > > > > > works: Kirill's (64GB machine) > > > > > > > Dave's RHEL7 host (24GB RAM, dual xeon, RHEL7 > > > > > > > userspace and kernel > > > > > > > config) > > > > > > > fails: Dave's f24 VM (4GB RAM, 4 vcpus VM on my laptop24 > > > > > > > userspace and kernel config) > > > > > > > > > > > > > > So it's any of userspace, kernel config, machine hardware or hmm. > > > > > > > > > > > > > > My f24 box has transparent_hugepage_madvise, where my rhel7 has > > > > > > > transparent_hugepage_always (but still works if I flip it to > > > > > > > madvise at run time). I'll try and get the configs closer together. > > > > > > > > > > > > > > Liang Li: Can you run my test on your setup which fails the > > > > > > > migrate and tell me what your userspace is? > > > > > > > > > > > > > > (If you've not built my test yet, you might find you need to add a : > > > > > > > tests/postcopy-test$(EXESUF): tests/postcopy-test.o > > > > > > > > > > > > > > to the tests/Makefile) > > > > > > > > > > > > > > > > > > > Hi Dave, > > > > > > > > > > > > How to build and run you test? I didn't do that before. > > > > > > > > > > Apply the code in: > > > > > http://lists.gnu.org/archive/html/qemu-devel/2016-04/msg02138.html > > > > > > > > > > fix the: > > > > > + if ( ((b + 1) % 255) == last_byte && !hit_edge) { > > > > > to: > > > > > + if ( ((b + 1) % 256) == last_byte && !hit_edge) { > > > > > > > > > > to tests/Makefile > > > > > tests/postcopy-test$(EXESUF): tests/postcopy-test.o > > > > > > > > > > and do a: > > > > > make check > > > > > > > > > > in qemu. > > > > > Then you can rerun the test with: > > > > > QTEST_QEMU_BINARY=path/to/qemu-system- > > > x86_64 ./tests/postcopy- > > > > > test > > > > > > > > > > if it works, reboot and check it still works from a fresh boot. > > > > > > > > > > Can you describe the system which your full test failed on? What > > > > > distro on the host? What type of host was it tested on? > > > > > > > > > > Dave > > > > > > > > > > > > > > > > > Thanks, Dave > > > > > > > > The host is CenOS7, its original kernel is 3.10.0-327.el7.x86_64 > > > > (CentOS 7.1?), The hardware platform is HSW-EP with 64GB RAM. > > > > > > OK, so your test fails on real hardware; my guess is that my test will work on > > > there. > > > Can you try your test with THP disabled on the host: > > > > > > echo never > /sys/kernel/mm/transparent_hugepage/enabled > > > > > > > If the THP is disabled, no fails. > > And your test was always passed, even when real post-copy was failed. > > > > In my env, the output of > > 'cat /sys/kernel/mm/transparent_hugepage/enabled' is: > > > > [always] ... > > OK, I can't get my test to fail on real hardware - only in a VM; but my > suspicion is we're looking at the same bug; both of them it goes away > if we disable THP, both of them work on 4.4.x and fail on 4.5.x. > I'd love to be able to find a nice easy test to be able to give to Andrea > and Kirill > > I've also just confirmed that running (in a VM) a fedora-24 4.5.0 kernel > with a fedora-23 userspace (qemu built under f23) still fails with my test. > So the problem there is definitely triggered by the newer kernel not > the newer userspace. OK, some more results - I *can* get it to fail on real hardware - it's just really really rare, and the failure is slightly different than in the nest. I'm using the following magic: count=0; while true; do count=$(($count+1)); echo 3 >/proc/sys/vm/drop_caches; echo >/proc/sys/vm/compact_memory; echo "Iteration $count"; QTEST_QEMU_BINARY=./bin/qemu-system-x86_64 ./tests/postcopy-test || break; done I've had about 4 failures out of about 5000 runs (ouch); On the real hardware the failure addresses are always 2MB aligned, even though other than the start address, everything in the test is 4K page based - so again this is pointing the finger at THP: /x86_64/postcopy: Memory content inconsistency at 4200000 first_byte = 48 last_byte = 47 current = 1 hit_edge = 1 postcopy-test: /root/git/qemu/tests/postcopy-test.c:274: check_guests_ram: Assertion `0' failed. /x86_64/postcopy: Memory content inconsistency at 4200000 first_byte = e last_byte = d current = 9b hit_edge = 1 postcopy-test: /root/git/qemu/tests/postcopy-test.c:274: check_guests_ram: Assertion `0' failed. /x86_64/postcopy: Memory content inconsistency at 4800000 first_byte = 19 last_byte = 18 current = 1 hit_edge = 1 postcopy-test: /root/git/qemu/tests/postcopy-test.c:274: check_guests_ram: Assertion `0' failed. /x86_64/postcopy: Memory content inconsistency at 5e00000 first_byte = d6 last_byte = d5 current = 1 hit_edge = 1 postcopy-test: /root/git/qemu/tests/postcopy-test.c:274: check_guests_ram: Assertion `0' failed. (My test host for the real hardware is 2x E5-2640 v3 running fedora 24) where as in the VM I'm seeing immediate failures with addresses just on any 4k alignment. You can run a couple in parallel; but if your load is too high the test will fail with an assertion (postcopy-test.c:196 ...(qdict_haskey(rsp, "return")) - but that's my test - so don't worry if you hit that; decreasing the migrate_speed_set value should avoid that if you're hitting it repeatedly. (Could this be something like a missing TLB flush?) Dave > > Dave > > > > > Liang > > > > > Dave > > > > > > > > > > > > > > > > > > > > > > > Thanks! > > > > > > Liang > > > > > > > > > > > > > > > > > > > > Dave > > > > > > > > > > > > > > > > -- > > > > > > > > Kirill A. Shutemov > > > > > > > -- > > > > > > > Dr. David Alan Gilbert / dgilbert@xxxxxxxxxx / Manchester, UK > > > > > -- > > > > > Dr. David Alan Gilbert / dgilbert@xxxxxxxxxx / Manchester, UK > > > -- > > > Dr. David Alan Gilbert / dgilbert@xxxxxxxxxx / Manchester, UK > -- > Dr. David Alan Gilbert / dgilbert@xxxxxxxxxx / Manchester, UK -- Dr. David Alan Gilbert / dgilbert@xxxxxxxxxx / Manchester, UK -- 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>