On Thu, 1 Dec 2011, Ying Han wrote: > The problem with small dmesg ring buffer like 512k is that only limited number > of task traces will be logged. Sometimes we lose important information only > because of too many duplicated stack traces. This problem occurs when dumping > lots of stacks in a single operation, such as sysrq-T. > > This patch tries to reduce the duplication of task stack trace in the dump > message by hashing the task stack. The hashtable is a 32k pre-allocated buffer > during bootup. Each time if we find the identical task trace in the task stack, > we dump only the pid of the task which has the task trace dumped. So it is easy > to back track to the full stack with the pid. > > When we do the hashing, we eliminate garbage entries from stack traces. Those > entries are still being printed in the dump to provide more debugging > informations. > > [ 58.469730] kworker/0:0 S 0000000000000000 0 4 2 0x00000000 > [ 58.469735] ffff88082fcfde80 0000000000000046 ffff88082e9d8000 ffff88082fcfc010 > [ 58.469739] ffff88082fce9860 0000000000011440 ffff88082fcfdfd8 ffff88082fcfdfd8 > [ 58.469743] 0000000000011440 0000000000000000 ffff88082fcee180 ffff88082fce9860 > [ 58.469747] Call Trace: > [ 58.469751] [<ffffffff8108525a>] worker_thread+0x24b/0x250 > [ 58.469754] [<ffffffff8108500f>] ? manage_workers+0x192/0x192 > [ 58.469757] [<ffffffff810885bd>] kthread+0x82/0x8a > [ 58.469760] [<ffffffff8141aed4>] kernel_thread_helper+0x4/0x10 > [ 58.469763] [<ffffffff8108853b>] ? kthread_worker_fn+0x112/0x112 > [ 58.469765] [<ffffffff8141aed0>] ? gs_change+0xb/0xb > [ 58.469768] kworker/u:0 S 0000000000000004 0 5 2 0x00000000 > [ 58.469773] ffff88082fcffe80 0000000000000046 ffff880800000000 ffff88082fcfe010 > [ 58.469777] ffff88082fcea080 0000000000011440 ffff88082fcfffd8 ffff88082fcfffd8 > [ 58.469781] 0000000000011440 0000000000000000 ffff88082fd4e9a0 ffff88082fcea080 > [ 58.469785] Call Trace: > [ 58.469786] <Same stack as pid 4> > [ 58.470235] kworker/0:1 S 0000000000000000 0 13 2 0x00000000 > [ 58.470255] ffff88082fd3fe80 0000000000000046 ffff880800000000 ffff88082fd3e010 > [ 58.470279] ffff88082fcee180 0000000000011440 ffff88082fd3ffd8 ffff88082fd3ffd8 > [ 58.470301] 0000000000011440 0000000000000000 ffffffff8180b020 ffff88082fcee180 > [ 58.470325] Call Trace: > [ 58.470332] <Same stack as pid 4> > > changelog v6..v5: > 1. clear saved stack trace before printing a set of stacks. this ensures the printed > stack traces are not omitted messages. > 2. add log level in printing duplicate stack. > 3. remove the show_stack() API change, and non-x86 arch won't need further change. > 4. add more inline documentations. > > changelog v5..v4: > 1. removed changes to Kconfig file > 2. changed hashtable to keep only hash value and length of stack > 3. simplified hashtable lookup > > changelog v4..v3: > 1. improve de-duplication by eliminating garbage entries from stack traces. > with this change 793/825 stack traces were recognized as duplicates. in v3 > only 482/839 were duplicates. > > changelog v3..v2: > 1. again better documentation on the patch description. > 2. make the stack_hash_table to be allocated at compile time. > 3. have better name of variable index > 4. move save_dup_stack_trace() in kernel/stacktrace.c > > changelog v2..v1: > 1. better documentation on the patch description > 2. move the spinlock inside the hash lockup, so reducing the holding time. > > Note: > 1. with pid namespace, we might have same pid number for different processes. i > wonder how the stack trace (w/o dedup) handles the case, it uses tsk->pid as well > as far as I checked. > 2. the core functionality is in x86-specific code, this could be moved out to > support other architectures. > 3. Andrew made the suggestion of doing appending to stack_hash_table[]. > > Signed-off-by: Ying Han <yinghan@xxxxxxxxxx> > Signed-off-by: Greg Thelen <gthelen@xxxxxxxxxx> > --- > arch/x86/include/asm/stacktrace.h | 11 +++- > arch/x86/kernel/dumpstack.c | 24 ++++++- > arch/x86/kernel/dumpstack_32.c | 7 +- > arch/x86/kernel/dumpstack_64.c | 7 +- > arch/x86/kernel/stacktrace.c | 123 +++++++++++++++++++++++++++++++++++++ > include/linux/sched.h | 3 + > include/linux/stacktrace.h | 4 + > kernel/sched.c | 32 +++++++++- > kernel/stacktrace.c | 15 +++++ > 9 files changed, 211 insertions(+), 15 deletions(-) > Looks like something that would go through x86/debug? Probably best to cc Ingo, Peter, and Thomas. -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>