* Ying Han <yinghan@xxxxxxxxxx> [2011-05-05 10:17:36]: > On Thu, May 5, 2011 at 2:21 AM, Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx> wrote: > > * Ying Han <yinghan@xxxxxxxxxx> [2011-05-04 10:14:04]: > > > >> 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 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. Then we hash the task stack with stack_depth 32 for each stack > >> entry. 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. > >> > >> [ 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> > > > > Given that pid's can be reused, I wonder if in a large time window the > > output can be confusing? The dmesg ring buffer can be scaled with a > > config option .. (CONFIG_LOG_BUF_LEN??) > > yes, we can always configure it to a larger value. however, it depends > how much duplications you might have and the buffer can be easily > filled up. this patch is useful which we can keep the same ring buffer > size but get more information out of by only doing > dedup of task stacks. > The dedup has a cost, given large memory systems and the ability to process some of these things in user space, does it make sense to do it there? Just a thought, since I've not seen a whole lot of duplication. -- Three Cheers, Balbir -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx 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>