2.6.38-rc1 problems with khugepaged

2.6.38-rc1-git1 runs normally with khugepaged switched OFF. Thus, khugepaged is the problem; as said if switched it on, during boot the computer becomes very slow and sticks almost. wl
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Sorry, looks like x86 32bit THP wasn't tested in all possible .config (32bit support is upstream-only feature and because of lower userbase it also got a lot less testing than 64bit support).

Does it make any difference if you both disable CONFIG_PARAVIRT and enable HIGHMEM64?

For now keep THP off on 32bit, it should be trivial to reproduce so fix will come soon.

Minchan info shows it's an 32bit arch bug so don't be too worried about it because it can't affect 64bit builds and it's not common code bug and we'll fix it ASAP.

Thanks,
Andrea

[ annoying plug ]

Just want to mention that ktest.pl was included in this release, just for this purpose :)

It does randconfigs (and other nice features) and will test various kernels. All you need is to have a test machine that can be remotely booted and have its console read via stdio from another machine.

This happened to be how I triggered the bug.

I would be happy to help anyone set it up. The config I used to test my box to do 10 runs of randconfig with a minimal config to make it boot, and then 10 runs of randconfig with the minimal config to make it boot and enable networking:

-----
MACHINE = mitest

# The TEST_START can override most defaults

# do ten boot tests (minimum forced config settings as possible)
TEST_START ITERATE 10
TEST_TYPE = boot
BUILD_TYPE = randconfig
MIN_CONFIG = /home/rostedt/work/autotest/configs/mitest/config-mitest-min
CHECKOUT = origin/master

# do ten boot and ssh hackbench tests (need network configs set)
TEST_START ITERATE 10
TEST_TYPE = TEST
BUILD_TYPE = randconfig
MIN_CONFIG = /home/rostedt/work/autotest/configs/mitest/config-mitest-net
CHECKOUT = origin/master
TEST = ssh root@mitest /work/c/hackbench_32 50

# defaults to use when watching test (SKIP will make ktest ignore it)
DEFAULTS SKIP
REBOOT_ON_ERROR = 1
POWEROFF_ON_ERROR = 0
POWEROFF_ON_SUCCESS = 0
REBOOT_ON_SUCCESS = 1
DIE_ON_FAILURE = 1

#defaults to kick off at night, and shut down at the end DEFAULTS
REBOOT_ON_ERROR = 0
POWEROFF_ON_ERROR = 1
POWEROFF_ON_SUCCESS = 1
REBOOT_ON_SUCCESS = 0
DIE_ON_FAILURE = 0
STORE_FAILURES = /home/rostedt/work/autotest/nobackup/failures

# defaults for all tests
DEFAULTS
POWEROFF_AFTER_HALT = 60
CLEAR_LOG = 1
MIN_CONFIG = /home/rostedt/work/autotest/configs/mitest/config-mitest-min
SSH_USER = root
BUILD_DIR = /home/rostedt/work/autotest/nobackup/linux-test.git
OUTPUT_DIR = /home/rostedt/work/autotest/nobackup/mitest
BUILD_TARGET = arch/x86/boot/bzImage
TARGET_IMAGE = /boot/vmlinuz-test
POWER_CYCLE = /home/rostedt/work/autotest/cycle-mxtest
CONSOLE = nc -d fedora 3001
LOCALVERSION = -test
GRUB_MENU = Test Kernel
MAKE_CMD = distmake-32 ARCH=i386
POWER_OFF = /home/rostedt/work/autotest/poweroff-mxtest
BUILD_OPTIONS = -j20
LOG_FILE = /home/rostedt/work/autotest/nobackup/mitest/mitest.log
TEST = ssh root@mitest cat /debug/tracing/trace
ADD_CONFIG = /home/rostedt/work/autotest/configs/config-broken /home/rostedt/work/autotest/config-general
-----

-- Steve

I reproduced your 32bit x86 problem with an initramfs with a hugepage benchmark placed as /init inside KVM (not exactly an extensive test but it was trivial to reproduce). I tested below fix with HIGHMEM4G and HIGHMEM64G with PARAVIRT=y (and verified setting PARAVIRT=n fixed it, in other email Minchan also verified that setting HIGHMEM64G=y also fixed it, to confirm my theory the problem was the below #ifdef).

The stress test reaches exit() successfully now (before the fix it crashed in out_of_memory() instead of do_exit as expected):

NMI watchdog disabled for cpu0: unable to create perf event: -2 �Kernel panic - not syncing: Attempted to kill init!
Pid: 1, comm: init Not tainted 2.6.37+ #17

Call Trace:
 [<c14351d2>] ? panic+0x57/0x161
 [<c107439b>] ? trace_hardirqs_on+0xb/0x10
 [<c1045321>] ? do_exit+0x6b1/0x6e0
 [<c10728ab>] ? trace_hardirqs_off+0xb/0x10
 [<c1045389>] ? do_group_exit+0x39/0xa0
 [<c1045403>] ? sys_exit_group+0x13/0x20
 [<c1002d9c>] ? sysenter_do_call+0x12/0x3c

QEMU 0.12.1 monitor - type 'help' for more information (qemu) quit

====
Subject: thp: fix PARAVIRT x86 32bit noPAE

From: Andrea Arcangeli <[email protected]>

This fixes TRANSPARENT_HUGEPAGE=y with PARAVIRT=y and HIGHMEM64=n.

The #ifdef that this patch removes was erratically introduced to fix a build error for noPAE (where pmd.pmd doesn't exist). So then the kernel built but it failed at runtime because set_pmd_at was a noop. This will correct it by enabling set_pmd_at for noPAE mode too.

---

index 2071a8b..ebbc4d8 100644
@@ -558,13 +558,12 @@ static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
 static inline void set_pmd_at(struct mm_struct *mm, unsigned long addr,
 			      pmd_t *pmdp, pmd_t pmd)
 {
-#if PAGETABLE_LEVELS >= 3
 	if (sizeof(pmdval_t) > sizeof(long))
 		/* 5 arg words */
 		pv_mmu_ops.set_pmd_at(mm, addr, pmdp, pmd);
 	else
-		PVOP_VCALL4(pv_mmu_ops.set_pmd_at, mm, addr, pmdp, pmd.pmd);
-#endif
+		PVOP_VCALL4(pv_mmu_ops.set_pmd_at, mm, addr, pmdp,
+			    native_pmd_val(pmd));
 }
 #endif
 

It works well in my system until kernel compile completed while dd if=/dev/sda3 of=/dev/zero and really slow web browsing.

Thanks, Andrea.

Kind regards,
Minchan Kim